How to install a membrane switch?

[philc]

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?

 

[Harald Kapp]

Some pictures will be of great help. Image size max. 300 kB uploads fine.

Pus some more detail about the "old guy" (make, model, ...)