https://wccftech.com/ios-12-lets-you-easily-rescan-your-face-on-the-lock-screen-if-face-id-fails/

iPhone X users are going to love this one. If Face ID fails on the lock screen, you can simply do a rescan using a swipe up gesture.

If you are running iOS 11 right now on the iPhone X then you already know how Face ID works. Just wake the phone, bring it up to your face and you’re in. In case the scan fails and you see the passcode screen, you have to either enter your credentials or just put your device to sleep and wake it up again for a new scan. Not exactly convenient. But with iOS 12, Apple has made an interesting change that makes things far more easier.