How to treat pectus excavatum without having surgery?

There is none: Pe is a structural deformity. Not all need to be surgically corrected, but if it is severe only surgery can correct it. There are no braces or exercises that can fix pe.

Pectus excavatum: Pectus excavatum can be surgically repaired, but surgery is usually reserved for people who have moderate to severe signs and symptoms. People who have mild signs and symptoms may be helped by physical therapy. Certain exercises can improve posture and increase the degree to which the chest can expand. http://www.mayoclinic.org/diseases-conditions/pectus-excavatum/basics/treatment/con-20028599