Knocked a tooth loose, anything i can do?

See your dentist: It all depends on how much if any damage there was to the tooth, including the nerve to the tooth. Only a dentist can asses the situation and give you a proper diagnosis.

Put it back in: Gently rinse out the tooth if there is dirt on it but don't scrub it and place it back into the socket where it used to be. Then get to a dentist immediately. If you can't place it back into the socket, hold it in your mouth. Third option is to place it in some milk, not water. Some teeth can be replaced but time is of the essence.