First, log out of Clay completely, then look for "forgot password" on the login screen and click it. You'll receive an email with reset instructions.
If you don't receive the email, you likely signed up using Google Authentication instead of a password. Try logging in via Google instead.
If the reset email still doesn't come through, check your spam/junk folder and ensure your email address is entered correctly.
If you want to switch from Google login to password-based login, you'll need to request human assistance by clicking "Talk to a person."