Rounded shoulder position will often lead to shorten structures downstream of the shoulder.
Remember spine first! Step number one is restore t spine extension.
Smash the anterior chest structures. While you’re at it.
Combine that with some heavy farmer carries to help strengthen posture and position. Emphasize retraction of your shoulder blades and extension of the arm so flex your tricep when your carrying heavy things.
Work upstream and downstream of the problem.
Voodoo floss and barbell smash the rest of the arm as much as you can take.