Either... A plastic surgeon or otolaryngologist (ENT) with experience in treating functional problems of the nose.
Nose doctor. If there are symptoms like nasal obstruction, snoring or recurrent sinusitis, have your nose evaluated by a board certified otolaryngologist.
Board Certified P.S. Great question. I would recommend consulting with a board certified plastic/cosmetic surgeon who specializes in surgical nose procedures, because surgery may be needed but that cannot be diagnosed here.
A nose specialist. Hi. Great question. Some septoplasties are very simple and some are much more complex. A good general ENT surgeon (otolaryngologist) should be able to straighten your septum. In more complex cases a facial plastic surgeon may be a better option. Occasionally you will find a plastic surgeon who understands the nose well enough to do your septoplasty but most do not specialize in that. Research!
Deviated Septum. You could see and otolaryngologist(ent), plastic surgeon or facial plastic ; reconstructive surgeon. In my opinion it is better to see someone with nasal experience. The rhinoplasty society would be a useful resource. Hope this helps.