Sit in your wheelchair with your feet resting on the footrests, and ensure the brakes are applied.
If possible, sit upright and pull your shoulders back with your neck long.
Place your heel of hand against the side of your head.
When ready, attempt to tilt your head to the side as though taking your ear to your shoulder, but match the resistance through your hand to result in a static muscle contraction.
Hold this position for the duration as instructed by your therapist.
Relax, and repeat.