You don’t It’s the natural way your body releases a build up of cum , so if you haven’t O in a while it’ll build up inside you & you have to have a wet dream to remove it from your body. It’s a good sign to be having wet dreams if you’re aiming to stop PMO and you don’t have any other form of sex (with someone).
It's a natural process. Don't fight it or feel guilty about it. Let your body look after itself and do what it has to do.