How can the indentation of my columella be fixed?

Hard to say without a photo but most columella indentations are caused by separation between the tip cartilages and are easily fixed with suturing. Other causes require different techniques.

The separation of the cartilage in this area is easily corrected with a tip-plasty by placing a cartilaginous strut between the medial crura of the tip cartilage that makes up the columella and then suture it together. There may be more that has to be done which would be determined by examination or a  picture.

Please share pictures to evaluate and could help you answer more specifically your question. There are many techniques to fix it.