If you mean a plastic/rubber ring with material stretched across, one
way is to bring opposite sides together, then fold the two loops into
each other, kinda. I haven't got it here so I'm working from memory.
Does that help?

Tom

the small ones practically fold themselves.  Wait till you try one of those
backgrounds that is 8 foot wide.

grab opposite sides and bring them together, make one hand slightly lower
than the other, the other two corners should start to turn inwards with
mickey mouse like ears, one slightly inside the other, just encourage that
folding.

or just twist and you will see something curl up underneath, just keep it
going and it will fall flat.  when you wrestle with a really big one you
don't that spring tension to keep that third side going and unfortunately
most of us don't have a third hand.