This is the situation: you must have disabled Face ID or Touch ID, yesterday . You don't have time to dig around in your settings while you work through a verification reset. If you are in a place where you think your own face or fingerprint will be used against you, use this trick to protect your iPhone immediately.
On your iPhone, press and hold both the Volume Up and Side buttons or Sleep / Hold / Wake button for about one and a half seconds. As soon as you see the "slide off" and "Emergency SOS" sliders (accompanied by haptic feedback), your iPhone Face ID or Touch ID turns off and you need your access code the next time you try to unlock it. However, once you have unlocked it, your iPhone will restore Face ID or Touch ID.
There is not just one way to force your iPhone to require an access code. Pulling up the standard shut-off screen does the same, but it takes about a second longer than the above method. However, if there is an advantage to the longer method, Emergency SOS does not appear as an option, so your risk of accidentally calling the police in a non-emergency situation is significantly reduced.
From the menu, on an iPhone with a Home button, hold down the Sleep / Wake button. For newer iPhones with Face ID, quickly press Volume up and then Volume down and then press and hold the side button.