If you forgot your password, you can click on the "Forgot password?" link on the sign-in window of CAPZilla or click this link.
You'll need to enter the email associated to the account. Note that some accounts may not have any emails associated to them and will require an admin delete and recreate the account.
If you forgot the email, then a new user will have to be created by CAP if no CAPZilla admin user is able to sign in to create a new user.
To create a new user from an admin account. See this article.