I realised today that I had no more front/back camera switch button anymore in the camera app. I tried removing app cache, rebooting the phone. I’m not really into selfies but I used the feature before and I know it was there, I just don’t know since when it disappeared. So now I cannot access the “selfie” camera.
I also downloaded another camera app (Open Camera) and I couldn’t find it there either.
Sounds like your top module is not connected well or broken. Try to #disassemble your phone and clean the connectors of the top module. Put it back making sure everything fits well.
If the option to switch to the front camera still doesn’t appear contact support for a replacement.