Quicksilver throttle only button replacment

[Tarpon1959]

How to I repaire the throttle only button? I have a button that was hard then difficult then failed. I have dissassembled it, looked at diagrams but quite frankly know how to get it out and fix it. I have attached a couple of pictures of my unit. Not quite sure of the model. Any help would be appreciated. The boat and motor are 1987, it is a merc 70.