Never try to force a prolapse back inside. You could cause further damage than has already been caused, and the gecko could possibly die. Try the sugar solution as it will pull the moisture out of the organ, reducing the swelling and allowing it to retract back inside. Mix water with ALOT of sugar, and make a paste out of it. You can also try a warm water soak and see if that will help. If you have any iodine or betadine, you can wash him with that to keep it clean, but just a antibacterial soap and water should work well enough, as well as the triple-antibiotic ointment.

If you try to force it back into a space where the organ cannot fit, you could rupture a hemipene or intestines and cause a hemorrhage. No vet could fix that. Just try the less invasive treatments and see what happens. If the organ starts to turn purple, black, or starts to have an odor, take the gecko to the vet immediately. This means that the tissue is not getting enough blood flow and is starting to die.

Hope he pulls through this ordeal. If he does, you may not want to put him back in with females, as this may happen again. I don't know if it is the same with reptiles, but in cattle and other animals, prolapses are hereditary and can be passed on to the offspring. I don't know if I would want that gecko passing that on to his offspring.