How do I get the "Unknown Part" message to stop?

A message about a non-genuine part is discussed in this support document: iPhone parts and service history - Apple Support

An Unknown Part message appears if the part installation is incomplete or if the part:

- Was replaced with a nongenuine part (e.g., you had it repaired with a third party service that did not use an Apple component)

- Was already used or installed in another iPhone

- Isn't functioning as expected

If the reason isn't immediately apparent, go to this page to find your nearest Apple Authorized Service Provider (AASP) or Apple Authorized Distributor (AAD) --> Find Locations

How to make a Genius Bar appointment

1. Go to Genius Bar Reservation and Apple Support Options - Apple

2. Go to "Get hardware help".

3. Select your hardware and continue selecting options requiring replacing parts until you see "Bring in for Repair"

4. Sign in with your Apple ID

"You will see a notification on your Lock screen for the first 4 days that you use your device and in the Settings app for 15 days. After that period, you can find the notification by going to Settings > General > About." - Apple Recommended reply by ASC contributor ckuan https://discussions.apple.com/thread/253100787?answerId=255812114022#255812114022

That’s really too bad. You should have had the repair done by an authorized service provider.

You can ask Apple if they will replace the screen properly, with genuine Apple parts, but don’t be surprised if they refuse to touch it now that it’s been tampered with.

The message serves as a warning that non-Apple parts have been installed by an unauthorized party.