Stand up straight with a resistance band attached securely to a solid object to the side of your affected arm.
Hold the other end of the band in your hand and lift your arm out to your side until it is horizontal.
Ensure there is tension in the band.
Keeping your shoulders relaxed to prevent hunching, pull your arm in to your side and across the front of your body against the resistance of the band.
Lead with your thumb.
Control the movement as you bring your arm back out to the side again.