"old passcode" pop up

my iphone XR is a recently new phone. when i made the apple id attatched i had forgotten the password and had to reset it. when i entered the phone again it keeps asking me every time i try to log into the apple id to enter the "old passcode", which i do not remember. i only have one device connected to it and i don’t know what to do because it won't let me use some features of my apple id if i don't enter it. is there anyone that understands this?