How do I adjust the walking belt if it shifts off-center?

First remove the key and unplug the power cord. If the walking belt has shifted to the left, use the hex key to turn the left rear roller bolt clockwise 1/2 of a turn. If it has shifted to the right, turn the left rear roller bolt counterclockwise 1/2 of a turn. Then plug in the power cord, insert the key, and run the treadmill for a few minutes, repeating the process until the walking belt is centered.