Lines on an iPad screen are usually a hardware issue, not something you can fix with settings—most commonly it’s a damaged display panel, loose internal connector, or pressure/crack on the screen (even if it’s not obvious). Sometimes it can be a software glitch, so a quick restart or update is worth trying, but if the lines stay or change when you press the screen, it’s almost always a screen or internal cable problem in my experience, that ends up needing a repair or screen replacement.