iPhone 8 added passcode and I don’t have one. All it does is lock for an hour.

My iPhone 8 came up with a passcode on my phone today. When this option came up all it does is lock the phone.I can’t see anything except enter passcode which I don’t know it.I call apple support and they walked me through getting it back to factory setting. But my computer is too old and error code 10 comes up and wants me to update computer which it is too old to take new updates.