From there you can repeat that square, practicing the movements slowly. Start again with rounding forward, trying to make it a little bit smoother now. Coming up, then back, keeping that elbow straight, flexing your tricep a little bit, and then sliding that arm down.
After you have gotten that, try to reverse it! Slide your arm back, lift your shoulder blade up, round that shoulder forward, and slide back down. You will want to try doing two to three repetitions each direction at least once a day to help with your shoulder blade mobility!