"Straight from the Xr2I manual"
1. Turn the transmitter power switch on.
2. Press the MODE key to access the Function Mode.
3. Press the MODE key until REV.NORM appears in small
letters to the right of the screen.
4. Press the CHANNEL key to select the channel to be
changed (ST = Steering, TH = Throttle). be sure to only change the th=throttle, if you switch the steering it will be backwards also.
5. Press the INCREASE or DECREASE keys to move the cursor
to the desired direction.
6. To exit the Function Mode, either turn off the transmitter
power switch or press the MODE and CHANNEL keys at
the same time.
Heres the link to the manual just in case you dont have it