Take the hand weight prescribed by your Physiotherapist in your target hand palm up
Using your unaffected hand, take the target arm and bend to 90 degrees
Take the assisting hand away and maintain the 90 degree position against the resistance
Sustain for the period of time determined by your Physiotherapist
Use the unaffected arm to remove the weight and repeat
Note this can also be completed with the target hand pressing into the underside of a table/desk with the elbow bent to 90 degrees (video not available)