Try tightening the nut one flat. If that doesn't work, you can try this:

If the water isn't too cold, try having someone in the pool, holding a large bowl over the return, while you work on it from the outside.

If it turns out that you don't have the rubber sealing washer on the inside of the pool, you can still use the bowl routine, but you will lose a little water while you quickly move the bowl long enough to slip the washer into place.