This mobility exercise is awesome for getting into the top of a top upper trap muscle that is tight and restricted.
Using 1 Acumobility ball against a rack, lean your upper trap into the ball. Then work the arm through full range of motion from overhead to behind the back. As your arm goes behind your back, try to pull your trap down. Find 2-3 spots in the upper trap area and do 8 reps on each spot, both sides.