iPhone X Passcode

My passcode is 4 digits. I normally use facial recognition but last used my passcode four days ago when I had to wear a face mask at the doctor's office. IOS 15.6 has been downloaded and it is now asking for a six digit passcode to proceed with the update.

When I open settings / Face ID & Passcode the first thing it asks me for is a six-digit passcode, and says I already have one failed attempt. So although I can still (for the moment) use my phone with Face ID, I have no idea how to reset my passcode.