Knee joint is most suitable for flexion and extension. You can pedal your bike empty, or you can tie your legs with a sling (appropriate height) and lie down to move your knees. Swimming is also good.

The simplest: put your hands on both sides of your knees, gently touch them up and down, gently press them inward several times at the joint points, and gently rub them up and down to press them inward. Then, the left and right hands are placed on the front and socket of the knee respectively, and the left and right hands alternately touch the front and socket of the knee several times, and the hands are gently pressed inward.

I don't know if I made myself clear. Eat less irritating food, drinks, tobacco and alcohol, and keep warm.