The best way to fix a collapse is to not let it get there in the first place. Unless the boat is simply pointing to high, it takes about three feet of sheet to reel in a collapsed chute whereas about 6 inches would do if the collapse is caught just as the luff is beginning to curl agressively.

Once the spinnaker has collapsed you just start reeling in spinnaker sheet as quickly as possible. If you are trying to reel it in but run out of sheet before the spinnaker is full, the boat is pointing wayyyy to high....sometimes it's necessary to try and point this high in distance racing but rarely should it happen around the cans (unless you've sailed too far from a mark or the race committee was late dropping c-mark and put it 1/2 way back up the course!).