Hi @Vix77 from what posts are on the forums about this - you can't reverse it. Once you link to Google account, you can't go back.
I.called Google they said they are updating the App. Ours is down also. Yesterday. Today it's out again. I called Google and they said they are working on it. Its now been since 2pm central time. Its now almost 6pm. It's ridiculous!!!! Since Google bought out Fitbit the App doesn't work good at all. It sucks.