I can't change my version of Java Edition it is stuck on the latest version

I can't change my version of Java Edition it is stuck on the latest version

What I expected to happen was...:
I went to the installations pressed the + button to add a different version i wanted to press on 1.15.2 as my realm is on there and not the new updated 1.16 version

What actually happened was...:
the version button didn't have any options pop up so im stuck on the latest release 

Steps to Reproduce:
1. loaded up java launcher 
2. went to installations 
3. Pressed the + button
4. went to versions
5. Wouldn't shoe up any other versions