I forget my password

The simple answer is you can't, and if you restart the phone you will need to enter your password to re-enabled Face ID. But what you CAN do is make an iTunes backup or iCloud backup (or both for extra reassurance) then follow these instructions-->If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support to restore the phone from your backup. This will remove the passcode and let you create a new one.

For backup instructions-->About backups for iOS devices - Apple Support

Forgot? Click below…

Click->If you forgot the passcode for your iPhone, iPad, or iPod touch, or your ...

Click->If you forgot the answers to your Apple ID security questions - Apple ...

Click->If you forgot your Apple ID password - Apple Support

Click->If you forgot your Apple ID - Apple Support