This is the most difficult step. Go slow. Take your time. Be careful.
Wrap the tube in the towel. This will protect your hand if something goes wrong and you shatter the glass.
Using the pliers, grab the plug. Put one end in the hole and the other end on the edge of the plug. Slowly work the plug out. Try not to tear the rubber, or pull on the cord.
Once you get the plug most of the way out, slow down and pay attention. The heating pad will come out and you will need to get it back in. Mine had a foam insert that was wrapped around a plastic tube.