I think you couldn't.
If you think you give a chance for him, try to put the sugar paste as many times as possible, and "if" it shrinks enough, use rubber glowes and lubricant to gentle put back in his place. If something go wrong during the process, it will be fatal, and you must ready to euthanize him ASAP. But to be honest... 95% that without vet, will be prolapse again.
*Vet tomorrow? In this case don't try to put back yourself. Hope will be turn out fine