How can I setup my Face ID

Settings>Face ID and Passcode>(Add an Alternative Appearance/Add an Appearance)

You should continue to a part that shows a circle and grey lines going out from it. Inside, you should see the camera. Move your face into the camera range. Move your head left and right. Some Bars on the left and right will turn green. Your goal is to turn all of them green by moving your head towards the edges by tilting your head toward the gray lines. You will do this twice.

If your phone has been repaired, there is a chance Face ID is disabled, but your phone should notify you.

 Face ID - iPhone and iPad models that support Face ID, Animoji, and Memoji.   *

Face ID on your iPhone or iPad Pro.  *

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.   -

How to use Face ID: