Side Mirror came off on 95 m3 please help

Ok
Someone hit me in the side yesterday and dented my passenger door and my side mirror popped off. It did not break and I think it should pop right back on but do not want to break it trying. Has anyone else had this happen? Any tips on how tog et it back on before I drive to the body shop tommorow to get the door fixed? If you could e-mail me at [email protected] if you could help it would be great.

Thanks
Again