Which procedure would help correct asymmetrical nostrils? (photos)

Looking at your photos seems to give the faint suggest of a subnasal scar, as one would have from a liplift procedure. If this is the case, that would explain any difference because of the amount of skin lifted into the nasal base. In any event, the difference between the two sides can be corrected.

Even when we look directly at the base of your nose, there is a very minimal asymmetry between your right and left nostrils. If you are looking to achieve lowering of both of your nostrils on front view, and perhaps for improved symmetry as well, microdroplet Silikon-1000 injections may be considered. I hope this is helpful! Sincerely, Dr Joseph

It is almost impossible to achieve nostril symmetry. Any attempts can lead to taking too much off one side and then going back to take some more from the other side. As this goes on permanent scarring with poor healing can lead to worst asymmetry than before the surgery was done.
Also, it is very important to remember that nobody will look at your nostrils from below. From the front view the nostrils don't look as asymmetric as from below. Unless the asymmetry is really obvious and disfiguring, it should be left alone.

Regards
Dr. J