How do I get rid of “unknown display” notification in my settings?

You do know this is a user-to-user technical support site operated by Apple? I’m just a volunteer here. If you do have a genuine Apple display unit and you are getting this message only Apple Support can reset it. You must be on your iPhone which is why you don’t see the link I mentioned.

So contact Apple Support and they can fix this.

Click on the Get Support link at the top right of this page to contact Apple Support.