anybody know how to fix the screen problem showing on picture

This is very common faulty contact of the LCD/LED screen module, easy to understand but not that easy to fix, as the Flex cable might stickered on the screen glass, hot gun would "repair" but come back soon the same problem. I am still working on it to find a permanent way to fix this, you can refer my instructable.com of a Yamaha piano https://www.instructables.com/id/YAMAHA-DGX-620-LCD-Fix-With-NO-Cost/