Simply click here and sign in using the login details (Facebook, PayPal or email) you originally signed up with.
If you are unsure which method you used to sign up, you can always request a password reset, by clicking on the Forgot Password link at the sign-in page.
You should then receive an email that allows you to reset your password and sign in via email.
Please be aware that Zip Biz is unfortunately not currently accessible through the Zip app.