How to calibrate the screen on an iPhone 8+ ?

Hi

Try a reboot press the side volume button up quickly then side volume button down quickly then hold the power button down until you see apple logo.

Go to books download ios 11.4 user guide it.s Free.

Cheers

Brian 🇬-1F1E7;

If there’s a problem your iPhone is still young enough to be covered by warranty. Contact Apple Support And get their advice, arrange a Genius Bar appointment if necessary to have your phone checked by Apple.

what kind of problems? if it is a software issue, restore with iTunes, if it is hardware get a repair?