Welcome to the garage.
You know which transmission it has?
The P0750 code has to do with the Low/reverse solenoid. First check if the fluid level is ok and the fluid isnīt burnt.
If that is ok, you will have to measure the wiring from the transmission controller to the transmission, to see if there is no open/shorted circuit. If that is ok, then its most probably the Low/reverse solenoid.