A valve cannot "slip down" if the valve spring/ retainer/ is all hooked up, the SPRING keeps the valve up. So if the valve is "slipped down" that means the clips must have come out?

You need to tell the whole story, here.

Also, KD tool used to make one that twisted to operate, it would work on many kinds of engines.

Keeping the valve up is easy with compressed air. Just take apart your compression gauge, or else make one from an old spark plug.

You sure you didn't break something or bend a valve?