Face ID on the iPhone X is no doubt impressive however sometimes a situation may occur where you need to put in your passcode, waiting for Face ID to fail just so you can get to the passcode screen is time consuming so to speed things up and unlock your iPhone X using the passcode keypad:
First swipe up as if you wanted to unlock your iPhone X.
If your face can’t be seen or recognized, your iPhone will display the words “Face ID” in the middle of the screen.
Instead of waiting a few seconds for your iPhone to display the keypad, simply tap on the Face ID label.
You will now be instantly shown the keypad where you will be able to punch in your passcode.
Original source: iDownloadblog