Wrist pronation (assistant resistance) (Forearm pronation strengthening, with assistant resistance)

Sit upright with a table in front of you.
Place your weaker arm onto the table with your elbow bent.
Ask your assistant to sit opposite you, and take their hand as if to shake hands.
Have your assistant apply resistance as you try to turn your palm to face downwards.
Return to the starting position and then repeat.
Aim to keep your elbow, shoulder and body still during the exercise.