Stand up straight with your affected arm straight down by your side.
Hold a resistance band, or pulley in your affected hand.
Ensure the other end is tied securely.
Stand sideways to the band with your unaffected arm nearest the attachment point, so that the band travels across the front of your body.
Keeping some tension in the band, step further away from the attachment, and then step back in.
Continue this movement, ensuring you keep your arm straight beside you.
Keep your shoulder blades relaxed throughout this movement.