Locked out. Phone asking for google password

A guy i know has an s6 edge +. He told me that even after hard reset, it still asks him for his google password, which he does not remember because when he setup the phone, he did it with a new gmail.
So, now that he is locked out, is the only solution to flash the stock firmware through odin? If yes, where can i find stock firmware for s6+? Is it the same as s6 firmware?

Thanks!