How do I reset Face ID on my iPhone 15 Pro Max?

OK you have SDP.

Try a few times see if it defaults to passcode.

If not then you may have to wipe the phone in Recovery Mode using a computer. Then restore from your last backup (or lose data)

If you can't update or restore your iPhone or iPod touch – Apple Support (UK)

You still need your Apple account and password.

(If you don't set the phone up again it will remain on your account for 30 days so you cannot sell it right away)

Settings, FaceID & Passcode, Reset face ID

If Face ID isn’t working on your iPhone or iPad Pro – Apple Support (UK)

You may need to turn off Stolen Device Protection if activated