If you don't remember your password, use 'Forgot Password' (found on the password page when you log in).
If you don't remember your email/username, go to password reset and enter possible email addresses you own. When you enter the right one, you'll get the message that the password reset email was sent.
Note: There are a few ways to sign up, e.g. with email, Facebook, or Apple. Try logging in with these to find your account.
