Hello. My name is***** can help you with your question. Since you are able to move the motor in both directions by reversing the plug, we know the incline motor is OK. So the problem would have to be with the motor control board. This is the board that controls the voltages sent to the motor to make it move in the correct direction.
You can find the board here:
If you have any problem getting it or any questions about installing it, please let me know.