If available, you can use a cable machine for this exercise.
Alternatively, fix a resistance band to a solid object above head height.
Sit in your wheelchair with the resistance band above you.
Place your feet on the footrests, and ensure your brakes are applied.
Hold one end of the resistance band in your hand above head height with your palm facing forwards.
Pick up the slack in the resistance band by wrapping it around your hand.
When ready, pull down through the resistance of the band and bring your elbow into your side.
Hold this position for the duration as instructed by your therapist.
Return to the start position, and repeat.