Set the rings somewhere between knee and hip height and get into a Rings plank position at that height.
Turn the rings out so that they are now facing forward, instead of being parallel.
While keeping the rings turned out, lower yourself down until your body is at least as low as your hands.
Then push yourself back up to the starting position.
Form tips
Keep the rings turned out the whole time. This will force you to work your shoulder external rotators, and to lean forward more, thus increasing the stimulus on your muscles.
Keep your Abs engaged and a posterior Pelvic tilt .