He's here to learn how to do it himself, and that's what these forums are for. Just get a freewheel, and thread it on by hand.. put the chain on, and take the bike for a ride, making sure to really put some torque on it to tighten it up. Make sure you grease the threads before threading it on. Then you're done. If you decide to take it off, you will need a freewheel tool, which do vary slightly.