Depends on what you want to do, connect another account to waze? Otherwise disconect waze from fb and thats all.

Conect another account in Android: Disconnect waze and fb, logout fb, remove fb account from device settings (accounts), remove waze folder, reinstall waze. Log in with user name, make sure to not connect with fb app first or add the same fb account to the device settings again. This works fine for me, maybe there is an easier way but i had the best experience with this. The first account in the device settings will be chosen by waze i guess. After starting waze you can choose another fb account if needed. For iOS i guess log out all fb apps and reinstall waze should make the job.

When I had issues with mine I had to delete the app and reinstall it.