Hi Darksheer

The stabilizer can be a bit tricky to master at first but with the D/R switch in the up position you need to move the left stick diagonally up to the left quickly. If it works you should hear a beep from the tank and it will then be working. If you don't get it quite right either the gun will fire or the orange flashing light will start flashing green. A bit of practice and it becomes a bit easier to hit the stabilizer though

cheers
Gorehound