the top pulls off and exposes a robertson screw. The bottom pulls off to expose another roberstson screw. The robertson screw head is square.
If you don't have a screwdriver for roberson heads, you'll want to add them to your toolbox.
I don't know where you can get the exact replacement for your broken switch... try this site:
https://www.jaycorvparts.com/ (notice the link to download their catalog)
Here is one that might match from Amazon:
https://www.amazon.com/JR-Products-1...002UC8MW4&th=1
Here is another from Amazon:
https://www.amazon.com/Single-Switch...78MR97Z3&psc=1