Most bike shops will have a threading die that can be used to "chase" (clean up) the damaged threads and that may fix your problem. The die will work if there is enough metal to reshape. If the threads have been damaged to the point the thread metal is gone the die can't fix it. If the fork and bike are particularly valuable or of sentimental value, a frame builder or someone who knows his way around a brazing torch can flow brazing brass over the damage area and cut new threads.