you need to replace the screen, it may stop working anytime, I had the same issue with my j7, I claimed warranty and replaced it for free. if you have not made any physical damage, then they may replace it for free.
Please follow the steps below to resolve the issue:- 1 Adjust the brightness of the device then check (Setting-->Display-->Brightness) 2 "Disable the “Show Screen Updates" option in developer options or completely disable the Developer options."{(Setting-->Developer options (If its available & highlighted)-->Show Screen Updates)} 3 Check third party applications if downloaded recently. Post which check in Safe Mode, if the issue still persists. For further assistance, register your concern in Samsung members app(click on “+“icon>send feedback>Error report/ Ask Questions)
