See A-Z of rehabilitation exercises
In case you cannot see the video, here is a still sequence -
Hip flexions include both an active component and a stretch. Sit on a firm table-height surface with one leg outstretched and the other resting on the floor.
Bend forward from the hip in line with the extended leg. Hold that position for a few seconds.
Sit upright again and repeat this 5 times.
Change position and repeat the sequence with the other leg.