How can I be stronger after a stroke using constraint induced therapy?

Simple. The unaffected limb is constrained, so the weaker limb is forced to work more, like patching the strong eye to strengthen the 'lazy' eye.
Brain changes. There is evidence that constraint therapy works by forcing the brain to pay attention to the paralyzed side after stroke. I find it does not work if someone has complete paralysis of the hand but will improve dexterity and coordination if there is still some partial function of the hand. It can be very frustrating and time consuming and will often take several months to see results. Good luck.