Do you need to get the motor running in the normal direction, or reverse it from the normal? What vehicle?

If it's getting it running in the normal direction, counter clockwise shaft I believe, it might be as simple as recalibrating/resetting the speed control, possibly with the channel reversed on the transmitter.

If reverse direction is required, if it's a gear diff car it might need the diff(s) flipped to get it back to normal. Even if the motor needs reversed with software or rewiring the sensor in addition to ABC, the timing advance probably needs adjusted/corrected.