If you are at all uncomfortable doing this then take it to a shop that will guarantee their work. But here is how I do it. Go to a local machine tool supplier like Grainger or Do-All and ask for a center drill preferably a size 2 or 3 - shouldn't cost more than a few bucks. This is basically a drill with a short starting section then has a built in countersink. the thing with it is it will not walk around like a normal drill bit. Try to centerpunch the center of the broken bolt then start drilling with the center drill until you get a nice stright hole started, then you can switch to the appripriate size drill for whatever size easy-out you can use in there. Off the top of my head I think it is a 6mm bolt so you will end up using about a 1/8" drill and a dang small easy out. If none of that works, you will just have to drill the bolt all the way out and install a helicoil.