Some people do use preparation H, or even Manuka honey (it's a special kind of honey with healing properties). If there's a soft egg stuck, that complicates matters.
It's 50/50, perhaps - ducks can get through prolapse if they get help soon enough. My Sechs had a prolapse over two years ago - egg was stuck - had to get her to a vet. They removed the egg, put in three stitches. Thank the Lord she went broody when I kept her in the dark (she found some eggs and started sitting on them). She was broody over two months, but that gave her time to heal.