[Alan Anderson]

You have several options for correcting your problem. The easiest one is simply to swap the left and right motor controls.

Are you using tank drive or arcade drive? If tank, you might have your joysticks swapped. Press a button on the left one and make sure the indicator on the Driver Station display shows that to be the joystick you expect it to be. If they're reversed, just drag them to the proper place in the Setup list.

You could negate the X axis in the code if you're using Arcade drive.

However, the correct thing to do is to go through the motors one by one and make sure the wiring matches the programming. If you run one motor at a time, is it the motor you expect to run? Does it run in the direction you expect it to? There are several places both in hardware and software where things can get swapped.