To stretch and relax the muscles which connect the shoulder to the front of the chest (pectoralis), as well as biceps and flexors of the hand.
Stand side-on to a wall, roughly a foot away, with the affected side closest to the wall. Place the hand of the affected side palm against the wall, slightly above shoulder height and slightly backward of the body. The fingers should be pointing backwards.
Simply rotate the torso away from the wall until a stretch is felt at the front of the shoulder/armpit/chest area. Do not rotate the head simultaneously. Hold for 20 seconds whilst breathing slowly and deeply then return to the start position.
If you experience unusual tingling in the arm or hand during the stretch, you can adapt the stretch by changing the start position. Place the forearm vertically against the wall from elbow to fingers with palm flat. The elbow should contact the wall just above head height. The stretch is then performed as above.