Toenail brown band. Corrective action.

Hello Dr, there is a dark brown vertical line on big toe nail at my toe. It started 5 years back as very thin line and now grew in width to between 2 to 3 MM wide (seems 2.5 MM in manual measurements). I cannot say if the growth was faster in recent times as it seemed regular growing in this peiod. There is no other symptoms. It starts from toe nail start and goes to full end. Band seems to appear fairly regular across nail. Please refer to images. There is slight pigmentation change visible at the base of the nail at band's end. However, it not visible at the front portion tissues if the nail. (Image attached) There is no history of injury or infection in this period or in past on this toe nail. There is no history of such incident in family. This queation came after reading about subungual melanoma. Can someone please advise what it could be and immediate corrective action.