There is a brass(?) contact pin coming up from the bottom. The pin's upper part is knurled and press fit into the green button's tube. The whole thing is held together like a hose on a hose barb, easy to push on but difficult to remove.
The assembly can got at by removing the screw under the start/kill switch. The start/kill assembly is held in that assembly with an 'e' clip. Careful :yikes:, there are a couple of small springs you don't want to lose. I was going to drill down to the pin to punch it out, but the spring-loaded center punch split the head on the green shaft ... punched the pin out.
ps, too bad you lost the spring ...