Shoulder rotations in supine (Shoulder external/internal rotation AROM, arm out to side, 90/90, supine)

Lie on your back with your symptomatic arm stretched out at approximately 90 degrees from the side of your body.
Bend your elbow to a right angle, as you proceed with the movement your fingers should be pointing up towards the ceiling.
Slowly rotate your forearm up and then lower it back down, keeping your shoulder blades against the surface throughout the movement.
Relax and repeat.