Lie on your back with your affected arm by your side.
Place a pillow or towel under your upper arm.
Ask your assistant to place a belt around your forearm, just below your elbow.
The belt should circle around your assistant's hips.
Ask your assistant to place one hand on the side of your upper arm, providing an inwards pressure.
Your assistant will then move their hips back a little, tensioning the belt around your upper forearm.
As they do this, straighten your elbow out.
Your assistant can help with this movement, applying a stretch as you straighten your elbow.