Jake Reeder (seen above) achieved an amazing transformation of his physique. He minimised the cosmetic extent of his case of Pectus Excavatum through weight training, some cardio respiratory training & stretching. 
If you analyse his transformation photo you can see a large growth in lean muscle mass. Jake gained muscle & lost fat simultaneously (yes this is possible). The development of a lean muscular physique does wonders for fixing the cosmetics of PE as a chiselled abdominal region will greatly reduce the magnitude of the rib flare and potbelly associated with pectus and then a developed chest will serve to disguise the actual indented chest itself. Furthermore, the development of  Jakes back serves to correct the kyphotic posture associated with Pectus which will pull his chest and shoulders into a better position helping make the chest look flatter.
Despite the insane physical changes the most touching part about Jakes transformation was the mental change he went through. He said "the program taught him the value of a positive mindset which has been one of the most powerful influencers in his life". This is beautiful because, how I define fixing pectus is developing your body so much that having pectus no longer negatively affects you. That is when you are free. That is when pectus is no logner a problem. You cannot drastically alter your bone structure and make your chest flat. The goal is simply to develop your body so much to minimise the prominence of the condition so much so that it no longer negatively affects you. To see Jake having gone through this physical and mental change is amazing. Well done Jake!