Lie on your back with your symptomatic arm stretched out at approximately 90 degrees from the side of your body holding onto a weight.
Bend your elbow to a right angle and then slowly rotate your forearm back towards the floor by your head, keeping control of the weight.
Make sure your shoulder blades remain in contact with the floor throughout the movement.
Return to the neutral position, and then repeat, trying to increase the depth of your stretch each time.