Hello, I want to fix the Face ID of my phone through Apple Support

See if anything here helps 

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

If Face ID isn't working on your iPhone or iPad Pro  *

Face ID not working.   -

Face ID not working' problems on iPhone.    -

Fix iPhone X Face ID Not Working.    -

Face ID Not Working.   -

If you live near an Apple Store, make a Genius Bar appointment to have the device/computer tested. Supposedly there is no charge for testing. Use 3rd link if not near an Apple Store or aren’t in the US. Take the original purchase receipt with you. Hardware Repair - Keeping Confidential Data Safe.  -

Genius Bar Reservation  -  US.    

Find a store.  -

Authorized Service Provider.  -

ASC YouTube for how to to schedule a repair at an Apple Store or Apple Authorized Service Provider – Apple Support

Try what is contained in the links I posted. If they don't work, you need to go to an Apple Store or an authorized Apple repair store