Below you have the code for the 7 segments display test. The code will hAve a few examples to show characters, numbers and also control each segment separatelly. We have two voids for that. One is to show an entire character or number and the other is to control each segment separatelly. Downlaod the code from below and also the Adafruit library from the next link.
/*  7 segment display with WS2811 drivers example code
 *   By ELECTRONOOBS
 *   Tutorial: https://electronoobs.com/eng_arduino_tut108.php
 *   Scheamtic: Tutorial: https://electronoobs.com/eng_arduino_tut108_sch1.php
 *   Code: Tutorial: https://electronoobs.com/eng_arduino_tut108_code1.php
 *   PCB: Tutorial: https://electronoobs.com/eng_arduino_tut108_gerber1.php
 */
#include <Adafruit_NeoPixel.h>        //Download it here: https://www.electronoobs.com/eng_arduino_Adafruit_NeoPixel.php
#ifdef __AVR__
  #include <avr/power.h>
#endif
#define PIN            6      //Pin for serial data
#define NUMMODULES     2      //Amount of modules (7 seg displays)
Adafruit_NeoPixel pixels = Adafruit_NeoPixel(NUMMODULES*3, PIN, NEO_GRB + NEO_KHZ800);
//Variables
int delay_time = 40;
void setup() {  
  // This is for Trinket 5V 16MHz, you can remove these three lines if you are not using a Trinket
  #if defined (__AVR_ATtiny85__)
  if (F_CPU == 16000000) clock_prescale_set(clock_div_1);
  #endif
  // End of trinket special code
  pixels.begin(); // This initializes the NeoPixel library.
}
void loop() { 
//Example 1
//Could show 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and a  b  c  d  e  f  h  l  o  p  s  u  x(DP)
show_char(0,0);       //module 0 show a 0
show_char(1,'a');     //module 1 show the A
delay(delay_time);    
show_char(0,1);       //module 0 show a 1
show_char(1,'b');     //so on...
delay(delay_time);
show_char(0,2);
show_char(1,'c');
delay(delay_time);
show_char(0,3);
show_char(1,'d');
delay(delay_time);
show_char(0,4);
show_char(1,'f');
delay(delay_time);
show_char(0,5);
show_char(1,'h');
delay(delay_time);
show_char(0,6);
show_char(1,'l');
delay(delay_time);
show_char(0,7);
show_char(1,'o');
delay(delay_time);
show_char(0,8);
show_char(1,'p');
delay(delay_time);
show_char(0,9);
show_char(1,'s');
delay(delay_time);
//Example 2
//Could control each segment separatelly from A to G and the DP
show_segment(0,'a');    //Turn on segment A from module 0
show_segment(1,'f');    //Turn on segment F from module 1
delay(delay_time);
show_segment(0,'b');    //And so on...
show_segment(1,'e');
delay(delay_time);
show_segment(0,'c');
show_segment(1,'d');    
delay(delay_time);
show_segment(0,'d');
show_segment(1,'c');
delay(delay_time);
show_segment(0,'e');
show_segment(1,'b');
delay(delay_time);
show_segment(0,'f');
show_segment(1,'a');
delay(delay_time);   
}
void show_segment(int module, int segment)
{
  int num_led = module*3;
  switch (segment)
  {
    case 'a':
    pixels.setPixelColor(num_led, pixels.Color(255,0,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'b':
    pixels.setPixelColor(num_led, pixels.Color(0,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'c':
    pixels.setPixelColor(num_led, pixels.Color(255,255,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'd':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,0,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'e':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'f':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'g':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'x':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(0,255,255));  //DP  G  NC
    break;
  }
  
  pixels.show();
}
void show_char(int module, char character)
{
  int num_led = module*3;
  switch (character)
  {
    case 0:
    pixels.setPixelColor(num_led, pixels.Color(0,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    
    case 1:
    pixels.setPixelColor(num_led, pixels.Color(0,255,0));  //B  A  C  
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
      
    case 2:
    pixels.setPixelColor(num_led, pixels.Color(0,0,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 3:
    pixels.setPixelColor(num_led, pixels.Color(0,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,0,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 4:
    pixels.setPixelColor(num_led, pixels.Color(0,255,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 5:
    pixels.setPixelColor(num_led, pixels.Color(255,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 6:
    pixels.setPixelColor(num_led, pixels.Color(255,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 7:
    pixels.setPixelColor(num_led, pixels.Color(0,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 8:
    pixels.setPixelColor(num_led, pixels.Color(0,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 9:
    pixels.setPixelColor(num_led, pixels.Color(0,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'a':
    pixels.setPixelColor(num_led, pixels.Color(0,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,255,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'b':
    pixels.setPixelColor(num_led, pixels.Color(255,255,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'c':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'd':
    pixels.setPixelColor(num_led, pixels.Color(0,255,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'e':
    pixels.setPixelColor(num_led, pixels.Color(255,0,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'f':
    pixels.setPixelColor(num_led, pixels.Color(0,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'h':
    pixels.setPixelColor(num_led, pixels.Color(0,255,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,255,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'l':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'o':
    pixels.setPixelColor(num_led, pixels.Color(255,255,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'p':
    pixels.setPixelColor(num_led, pixels.Color(0,0,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,255,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 's':
    pixels.setPixelColor(num_led, pixels.Color(255,0,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,0,255));  //DP  G  NC
    break;
    case 'u':
    pixels.setPixelColor(num_led, pixels.Color(0,255,0));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(0,0,0));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    case 'x':
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(0,255,255));  //DP  G  NC
    break;
    
    
    default:
    pixels.setPixelColor(num_led, pixels.Color(255,255,255));  //B  A  C 
    pixels.setPixelColor(num_led+1, pixels.Color(255,255,255));  //E  D  F
    pixels.setPixelColor(num_led+2, pixels.Color(255,255,255));  //DP  G  NC
    break;
    
  }
  pixels.show();
}