If it turns CCW and does not back out, and you cannot get vise grips on it to apply some outward pressure, try a small flat head and gently pry the head up as you turn it CCW. Hopefully that will allow a good thread to catch. Then you can try the correct size tap to clean up the threads. If that tap does not do the trick you will need to drill the threads out and re-tap larger, obviously using a new larger screw.
Good Luck!
Rufus