Different sidewalls of the nose, is it fixable?

I would start by saying that facial asymmetry is universal and that there is no genuine midline of the face, so even the straightest nose has some degree of deviation depending on what you use as reference. That being said, 
It is possible in general to create the impression that the nose is reasonably straight.
If you feel further correction is needed, your first option would be to use injectable filler on the concave side to see if it gives you sufficient correction. This may however produce too much widening of the bridge.
In terms of surgical options, high septal deviations are more challenging and I find that ultrasonic instruments open more avenues for correction.
In consultation, it is possible to evaluate the anatomy and on a computer simulations to understand better what you would describe as a straight position of the nose, which would allow assessment of feasibility.

Sometimes differences between the left and right sidewall can be improved with small amounts of nasal filler.