How do you rehabilitate a paralyzed left side?

One should seek a professional therapist for this. Exercising in a swimming pool is the best way to gain the strength because water makes the body more buoyant and the person with paralysis has an easier time doing the exercises in the water. If you can't afford a therapist then ask someone to go with you into the pool and do very light exercises with the legs and arms and when you notice some mobility returning you can pump up the volume and do stronger exercises. Always check with your doctor first.