The digit write signal is not strong enough to activate the trigger of the missile launcher.
How does it work?
The yellow and white wires are connected to the DC motor behind the turret. As the motor rotates, it will trigger the mechanism to release a missile. The missile is mounted onto a pan and tilt servo mount. The joystick position is mapped to the turning degrees of the servo.
When running the program, you will find that when the power is supplied through the USB of the micro: bit, the power is not strong enough to drive the 2 servos. Just connect the power to the vin of the micro: mate instead.
Use the button of the joystick to fire instead of button A of the micro: bit. The connections will remain the same except we need to connect another cable from joystick sw to micro: mate pin 12 (green).