In your main while(1) loop add this:

HAL_GPIO_TogglePin(LD2_GPIO_Port, LD2_Pin);
HAL_Delay(500);

Easy peasy

A more complex example would be something like:

 while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
	  // Turn on initially
	  HAL_GPIO_TogglePin(LD2_GPIO_Port, LD2_Pin);
	  char morse[] = "- .... . / .-.. . .- -.. / .. ... / - .- ... - -.--";

	  for (int i = 0; i < (sizeof(morse)/sizeof(char)) - 1; i++) {
	      switch (morse[i]) {
	          case '.':
	              HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_SET);
	              HAL_Delay(100);
	              HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_RESET);
	              HAL_Delay(100);
	              break;

	          case '-':
	              HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_SET);
	              HAL_Delay(300);
	              HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_RESET);
	              HAL_Delay(100);
	              break;

	          case ' ':
	              HAL_Delay(200);
	              break;

	          case '/':
	              HAL_Delay(600);
	              break;

	          default:
	              break;
	      }
	  }

  }

That’s all I got Thanks