I would pay somebody to do it for you. I am assuming if you need to ask, you have no experience and could end up in trouble. calling out an engineer to put right a half finished job could end up being a lot more expensive. It is not technically difficult, but very awkward. a decent engineer should do it in 20 mins or so, and I would not expect you to be charged much more than £20, altough it has been several years since I have worked in this industry. Shop around. you might even get it done a bit cheaper.
Smiling carcass, August 2005