So how do I solve that

Are you getting a notification/message that the display on your iPhone is not genuine? Did you just get the display replaced from a third-party repair shop that uses after market products? If Yes, then the message is to let you know that your display is not an Apple genuine part.

The warning is informational only and will not affect the ability to use your ‌iPhone‌ or your display. A notification will be displayed on the Lock screen for the first four days a device is used following the repair, and in the Settings app for 15 days after that before being limited to General > About.

Axel F.