Resisted thumb palmer abduction - forearm in neutral

Sit upright in a chair.
Place your affected arm on a table with your hand on its side.
Wrap a resistance band around your hand in a figure of 8, crossing it before wrapping it around the base of your thumb.
Move your thumb forwards from your hand, keeping it parallel to the table, stretching the band as far as you can.
Control the movement as you bring your thumb back in towards the start position.