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 included allen wrench to turn the left rear roller adjustment 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. Plug in the power cord, reinsert the key, and run the treadmill for a few minutes, repeating the adjustment until the belt is centered. (Page 27)