Will masseter muscle exercises help? (Photo)

It is highly unlikely that selectively chewing on the smaller side will improve symmetry. You can attempt this but I would be surprised if it makes much of a difference. Botox treatment to the larger, hypertrophic side can create a reliable improvement if needed. I hope this information is helpful.Stephen Weber MD, FACSDenver Facial Plastic Surgeon

Exercise will not improve your master muscle asymmetry but Botox injections into the bigger side will.

Your masseter is one of the strongest, if not the strongest, muscle in your body.  It is unlikely that massage will change it.