How do I unlock My phone my face recognition

See Set up Face ID on iPhone https://support.apple.com/guide/iphone/set-up-face-id-iph6d162927a/ios

And see If Face ID isn't working on your iPhone or iPad Pro https://support.apple.com/en-us/HT208114

If after following the first seven steps given, "... you still need help, reset Face ID, then set it up again. Go to Settings > Face ID & Passcode and tap Reset Face ID. Then tap Set up Face ID to set it up again. 

If you can’t enroll your face, take your device to an Apple Retail Store or Apple Authorized Service Provider or contact Apple Support." You'll need to contact Apple Support  at this time unless an Apple Store is open in your area. If one is open, you can make a genius-bar appointment (https://www.apple.com/retail/geniusbar/) if you want.

The iPhone 8 does not have Face ID technology.

See the Apple Support article(s) below.

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