Deviated septum surgery cures bad breath?

Perhaps: If you have impeccable oral hygiene, a healthy mouth, and have regular dental care so a breath odor is not dentally caused then this is possible. Chronic sinus infections can be a cause of bad breath.

Of course: Any blockage of nasal passages can lead to more mouth breathing, dry mouth and bad breath so a deviated septum and similar can cause such as well. Septoplasty is the appropriate procedure to improve breathing and bad breath.