If you are the type who can fix things, open it up and you will find a small wire spring that was rattled off a lever when you dropped it. If the lever doesn't have spring return the T and B won't work. Very likely all it needs is someone to tip it back where it needs to be with a tooth pick. Anyone who can repair a clock work can get this done for you.
If not, I have a good working usable Betax 4 that I boogered the lens it once held.