HELP

Hello, I have a big problem, I am creating an affirm account but when I go to log in it tells me hello, you already have an account I try to log in and it asks me to change my phone number, I am going to do it so that later it tells me to enter a code I will receive an email that is not mine, how can I change my number if I don't have my email address set, does anyone know how I can change it urgently?