Can I get this Apple Face ID back

This Apple support page explains what to do to try to get Face ID working again.

If Face ID isn't working on your iPhone or iPad Pro - Apple Support

This iPhone User Guide describes setup and use of FaceID on supported models of iPhone:

Set up Face ID on iPhone - Apple Support

If FaceID isn't working, or has been disabled, you’ll need to follow this guidance:

If Face ID isn't working on your iPhone or iPad Pro - Apple Support

If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support

If you unable to resolve a problem, you would be well advised to seek assistance directly from Apple Support:

Official Apple Support

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your device. If a fault is confirmed, you'll be in the best possible place to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple