If you don't remember your password, use password reset.
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, phone number, Facebook, or Apple. Try logging in with these to find your account.
Our Community has more ways to find lost accounts.