Sit in an upright position, holding a resistance band in the hand of your affected arm with the other end secured to a solid anchor behind you such as a the chair back or a door handle.
Have somebody hold this if needed.
Place your affected arm out on a table or work surface at approximately 90° to your body.
Bend your elbow to a right angle, and hold the other end of the resistance band in your hand.
Maintaining good posture and shoulder blade control, rotate your arm upwards so that your forearm moves off the table from horizontal to vertical.
Your elbow should remain at a right angle and your posture should remain straight with your shoulder blades pulled back and kept down.
Pull against the resistance band and then return to the start position and repeat.