DON’T ROW YET
A common recommendation for improving posture is to row. Yet you can row until you are blue in the face but, unless you have excellent thoracic mobility, you will fail to balance out your development and could get hurt in the process. Does it make sense to load a movement one cannot perform without extra load? Would you put a barbell on the shoulders of a person who cannot do a single competent bodyweight squat?—The answer, of course, is no. By the same token, if you are unable to open your chest up with no external resistance, you should not be rowing with weights.
FIRST: SOFT TISSUE WORK
You need to overcome the fascia’s and other tissues’ internal resistance first. Various soft tissue work will help. So would a stretch with a yoga block. Lie down on the floor with a wooden block the size of a brick under your upper back. The block is strategically placed at a specific spot to ensure that you are stretching where it should. You need to hang out there for a long time to allow your shortened tissues to ‘ooze’ over the block. The head is supported by a folded towel that limits cervical extension and lets one hang out longer. Many minutes later, slowly roll to your side rather than sit up. There are subtleties to this. You are well advised to see a yoga expert.