How do I replace the pull rope on my bl100 trimmer? I know how to install it just not how to get it to rewind.

You are going to need to "preload" the spring in your recoil/starter unit BEFORE you install the pull rope. Turn in in the direction where you feel it becoming tighter. Turn it about 5-7 revolutions. Don't get carried away and make it REAL tight as you will break the spring steel recoil spring. After you have it set, jam it or hold it with vise grips or a screwdriver or with your hands and have someone install the pull rope. Make sure the handle is installed on the end of the pull rope before you begin because when you let the recoil pull your new rope in the handle will stop it. There should be a little bit of tension left on the pull rope once it is drawn in all the way.