Do this exercise its going to get you to unhunch your shoulders and pull your shoulders blades back.
Get on the bench with a couple of dumbbells and lengthen your legs with a slight knee bend so that you can grip your toes into a bench and then row the dumbbells up wards away from your shoulders and inwards to wards your ribcage below even to as low as the waist so that you hit your lats more than your traps.
The lower part of the midback not the upper part of the upper back and shoulders. The other tip you want to focus on is slowly decelerating the dumbbell downwards and it will be safer on your shoulders and also when you pull it up the dumbbells by the waist keep them up for a couple of seconds squeezing your shoulders blades back and together so that the muscles all of them from lower to mid to upper back all create a line down the length of the spine.
For people with really tight shoulders that must start opening more now with me I like to get you to use one arm at a time focus in on lifting the mid back and the sternum while alternating each arm so you are pulling one arm at a time.