How to get my iPhone Face ID

Have a look at these two articles -

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

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

If Face ID isn't working on your iPhone.

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

If you get a message that Face ID is disabled, this is most likely a hardware issue. Please update your iPhones software to the latest version, and if this is not working, Contact - Official Apple Support to set up service for your device