I got a rim job once. It was pretty good too. First you gotta get all the air out to make a gap that’s big enough. A big ass gap. Then you get some thick slimy goo lube and you get the big ass gap well lubed so you can stick all sort of sticks in the gap. You just want to pry that big ass gap open. If it was clean you could probably use actual jelly and then lick it off. Usually you want to get in there and get the old rubber off so you can get the new rubber on. In and out and back on. Easy and smooth.