To replace the belt on your Rug Doctor, start by turning off the machine and unplugging it. Locate the belt cover on the side or bottom of the machine and remove it using a screwdriver or by following the instructions in the user manual. Take note of the belt's position and tension before removing it. Install the new belt by following the provided instructions or consulting the user manual. Ensure the belt is properly tensioned and positioned before reattaching the belt cover.