Cause and Solution for Nose Indented on One Side?

The problem is not in the septum it is the position of the upper lateral cartilage that lies between the nasal bones and the tip cartilages. It is most likely due to some external trauma- a knock on the nose. The doctor first needs to look inside the nose and make sure there is no internal valve collapse with inspiration. If the valve is ok the best way to address it is by camouflaging it.
My first choice is crushed cartilage taken from elsewhere on the body such as behind the ear because it is permanent, easy, and gives a smoother result. You could use an injectable filler but these tend to not be permanent solutions and have a risk of being less smooth -- a lump.
If the valve is collapsing the solution is more involved but still doable.