Take a screenshot. View the screenshot, but make sure to slide the picture to the right so you viewing that section of the picture at a point where the screen looks Ok. Or view the screenshot on an external display or another device. If the vertical band appears does not appear in the screenshot, then the built-in Display Assembly is bad and will need replaced.
FYI, it is better to refer to that as a vertical "band" than a line since a line implies something thinner.
In the future please rotate your pictures before posting them online since it is very hard to observe them sideways. If the pictures are taken on an iPhone or iPad, then it is easy to rotate the picture on the iPhone/iPad by selecting the "Edit" option when viewing the picture.
https://www.iphonelife.com/blog/5/tip-day-how-rotate-photo