You can stretch your shoulder blade and relieve shoulder blade pain at home by following these steps that worked for me.
Take your right arm and reach straight up, then bend your elbow and let your hand fall behind your head.
Then move your left arm behind your back and bend your arm, then let the back of your left hand rest against the right shoulder blade.
Lastly reach to grab your right fingertips with your left hand.
Then repeat this exercise with your other arm to stretch and exercise your shoulder blade.