Stuck or dead pixels stuck on a color that don’t refresh with screen redraws. To overcome this problem there is a web app called Pixel Fix for iPhone, that’s intended to aid you in correcting stuck/dead pixels on your iPhone screen.
The developer of this app recommends you to consider the following two points while you’re testing for dead/stuck pixels:
1: Adjust your screen brightness to high.
2: Rotate your screen to check pixels in landscape and horizontal view.
The app developer doesn’t guarantee that this app will remove/unstick your iPhone stuck pixels but still giving it a try would be a nice move.
Link: Pixel Fix for iPhone