Insulate the bullet connectors befor going any farther. My best guess is that they touched and got some mosfets good 'n hot.

The paperwork covers programming through your transmitter. It works fine through my 3 series Spektrum.

To enter programming mode:
Turn transmitter on.
Set throttle & reverse (brake) throw to 100% if they aren't already. Brake % is switch E on your transmitter.
Connect car batteries.
Pull trigger full throttle forward and hold.
Switch MGM on.
Wait 10 seconds for 3 beeps.
Hold full reverse.
Wait for single beep.
Release throtthe.
Wait for two beeps.

You have calibrated your throttle throw and are now in programming mode.
If it were my choice I would switch the MGM off now to leave program mode and try again.

Program instructions are in your MGM paperwork but generally once in program mode:

Pull full throttle forward to bypass any parameter you do not wish to program.

Pull full reverse to progress through values within a parameter.
Full throttle then saves the selected value and moves to the next parameter.

Turn power switch off to exit program mode once your changes are saved.

As a bare minimum read the chart on page 6 of your MGM documentation.