...with the dent facing the fire. Check semi-frequently to make sure it doesnt get tooooo hot, but nice and warm for sure. Many times you'll be laughing with your friends not paying any attention and you'll hear it pop back on its own. If not, as Leland pointed out, push with a blunt object while warm.
Of course, it all depends on how bad the dent is. If it creases and shows stress discoloration, apply much duct tape and wait to work on it at home. This generally only happens in a bow or stern piton or in the case of a twist or fold while pinned.