First check the Lock switch directly below the Quick Control Dial. If it is enabled, the rear dial will not respond. Set the switch to the unlocked position, aligned with the white mark on the back of the camera.

Because the provided answer points to the lock switch as the cause, that is the first and safest thing to verify before considering any disassembly. Opening the camera to clean under the dial is not recommended unless you are experienced with camera repair, since it can cause further damage.