I want to have Face ID on iPhone

Hello,

Apple has several documents helping you with Face ID.

How to set up and use Face ID is described in this support article --> Use Face ID on your iPhone or iPad Pro - Apple Support and this one Set up Face ID on iPhone - Apple Support

- including how to turn on

This Support article is specific to seeing a 'disabled' Face ID alert, and explains what to do when you see that notice or an issue with the TrueDepth camera. --> If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support

Unless a software update solves the problem you may need to have Apple take a look at your device. Use this link to set up an appointment —> Genius Bar Reservation and Apple Support Options - Apple and this one to get a repair estimate —> iPhone Repair & Service - Apple Support

If you don't see a 'disabled' message but do have general issues with Face ID not working properly, explore the list of things to try in this document: If Face ID isn't working on your iPhone or iPad Pro - Apple Support

If the first 8 don't solve the issue then use #9, contact Apple.

If your Face ID is disabled this is most likely a hardware error. Please update your iPhone to the latest avaliable software version for your iPhone and if this is not working, please Contact - Official Apple Support to set up hardware service for your device