The correction of your deformity will be obtained by progressive re-education of bad posture. It includes:
General relaxation of the whole body.
Try and get the feel of the correct posture passively by a physiotherapist and learn to maintain it at regular intervals till correction becomes automatic.
Free mobility and strengthening exercises for your chest.
a) Shoulder shrugging - Shrug your shoulder. Hold and relax.
b) Shoulder Bracing - Keep your elbows bent with palms facing upwards. Push elbows back. Hold and relax.
c) Shoulder circling -Keep your fingers on shoulders and rotate elbows in circular manner.
d) Deep breathing exercises.
e) Keep a book on your head and walk straight, balancing the book.
I hope these tips help you to overcome your problem.