As there's no pics, i'm making a few assumptions but hopefully this might help. If it's the drive side, there should be a bit of a lip to stop it winding all the way in. Might be able to get a pair of grips round it or maybe file a couple of flats in it and put it in a vice? If the main bottom bracket is already out and it's the non drive side cup left in there you can get a big fat nut n bolt (I mean BIG) with the right size washers to tighten down on both sides of the cup (hope that makes sense). Keep tightening the bolt from the drive side and eventually the cup should wind out.