What to do if face id is disabled?

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

If the issue persists, contact Apple Support directly, using this link:--> https://getsupport.apple.com/?caller=kbase&SG=SG003&category_id=SC0999&symptom_id=23303 , or make an appointment and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

Disabled Face ID alert on your device

The link on top of this page, under the "Related Article”, please read --> "What to do Next" section to understand the process. If that link did not help then please mention the exact difficulty faced by you.