A microswitch button body has two holes on it for a couple of plastic pins to hang onto it.
Below is a couple of microswitches....you'll see the difference where the holes are.
If the plastic pin that's suppose to go into the switches holes are broken, it cannot hold the switch.
You may have to place a WTB ad in the Classifieds section of NLG to get another button or shop around.
Take good photo of the broken button and microswitch you have.
I'm sure someone will have one laying around.
If you have the ones like in the 3d photo below, then see if the microswitch isn't pushed up all the way into the button body like the other ones.
Pictures will tell us a better story.