How can I fix the spin/zoom button?

I bough a used Apple Watch 2 and love it but about 2 months afterwards I had a problem with it. Some black rubber came out of the side top button. Nothing happened for about another month then it would constantly zoom in and out without me touching the button. I couldn’t do anything with it. I watched the tear down video and have an idea on what came out but need some other ideas on what I should do and or how to fix it.