How to fix iphone 6s plus screen shadows?

So i just got an iPhone 6s plus 64 GB and its amazing but there are shadows of the bottom part of the home screen on other apps its very faint and also i can only see it on dark themed apps but its a little annoying can some one help? P.S (its pre owned if that helps)

Screen might be damaged. Contact a repair facility.

It's called burn-in, and it's a problem if your iPhone has the Samsung built panel. I'm guessing the phone is second hand, in which case to replace the screen is going to cost!