The potentiometer is located inside the foot pedal assembly. It’s purpose is to communicate the foot pedal motion to the wheel controller to adjust the speed of the wheel head. These are fairly robust components however they can get damaged if they get wet or the cord leading to the foot pedal gets put under abnormal strain.
If properly lubricated with anti-seize, your wheel head should come off easy with a twist and pull motion. Occasionally people will mistakenly remove the anti-seize thinking it is dirt or clay and this causes the wheel head to stick. Follow these instructions to remove the wheel head and reapply the anti-seize.