I've read numerous other answers for this, but I thought it was worth posting the same question with an addendum..
I actually solved this exact same problem once before by adding the correct images in my images.xcassets window, however I don't recall how I figured out which boxes to put the image in? How do I link the errors to the correct box?
Are you using Cordova? I see you tagged it but have no mention of it?
If you are just to save you some time and effort theres a really good npm plugin that generates all this for you & my xcode picked up all the different sizes automatically. cordova-icon.
It's really simple, just have an
icon.png in your root and run
cordova-icon in your console. It generates icons for android iOS and windows.