It is possible to fix, as it is unlikely that the spring is damaged (they are either OK or snapped). All you need to do is get a few more coils of cord around the mechanism (where the cord sits when it is retracted), so that there is more tension from the spring, pulling all of the cord back into place. Unfortunately it is way too difficult to describe how to do do this without diagrams. All i will say is that you need more of the cord wrapped around the internal mechanism when there is no force on the cord (when you let go). I have done this many times when fixing a pullstart, and once you get the knack it is easy, but if you have no idea what i have just said then forget it and buy a new one.