Here is a quick 10 minute workout for your shoulders and upper back. You need a resistance band - not too strong, for this workout. Either a circle band or a long one tied in a knot.
There are 4 exercises in this workout, 12 reps of each and 1-3 rounds. (I do 3 in the follow along video below).
1. Pull apart with palms down
2. Pull apart with palms up
3. Pull apart and lift overhead (palms facing each other)
4. Pull down and apart (palms facing each other)