Even though your tendon may have healed, it may also have scar tissue, and not have the range of motion it used to. Here is a website that may help. I’m guessing this is something for a physical therapist. For that, you may need a doctor to prescribe the exercises you need. Barring that, when it heals again, try stretching it, little by little, and ice it down afterward. Be sure to keep in shape while waiting for your body to cooperate. I’d stay off the skate board until you have it all stretched out again.