How to install a membrane switch?

I have an old medical device with me but the old guy keeps chocking these days. And the switch just popped out of it, I called the service provider but as it is old they excused my query. I have went through YouTube and other resources but failed to find a solution. Can anyone help me?

do you only have one or it's part of an array ?

at the end of the day it's usually just a switch but the membrane usually plays as a seal for the "button" which might be desired.

A great deal more detail is required and as a medical device is involved them be aware that members may be reluctant to provide advice because of the possible repercussions should anything go wrong

Please post more details of the device, including photos, and the problems that you are having