If forward and reverse are fine but your left and right are reversed then your motors are plugged in backwards Swap them and that should fix that issue. For the firing you might want to check the contact switch on the back of your airsoft unit, if the switch is touching it will continuously fire. Try to fire the tank a few times, it might stop. The contact switch is pretty sensitive with our system so just be aware of that. You may need to open the contacts a bit if they are touching, but there is a better chance it is just stuck in the middle of a recoil, hence trying the firing sequence once or twice to try and reset it.
The plug beside the power is for the High or Middle mount motor gearbox while the outside plug is for the Low mount gearbox. Hope this helps!