Two thin black vertical lines on the rear LCD usually indicate a fault in the LCD panel itself. In most cases this is a screen defect rather than a problem with the image being captured, so it typically will not appear in your photos.

If you’re not experienced with camera repair, there isn’t much you can safely do yourself beyond confirming the issue is only on the display. The practical options are to keep using the camera if the lines are only a viewing annoyance, or have the LCD replaced by a repair service if it bothers you enough to justify the cost.