As far as I know, from login perspective, the DSM16 devices work exactly the same way as UCX servers.
From a local subnet, you login into a new device using the default password and change it. The first time you log in, you are presented with the page where you can change the password (that page is most likely where the Cancel can be used as suggested by curlycord). If you cannot log in for some reason (e.g., you forgot the password), you can contact E-MetroTel support to reset the password. That gets you to the first step - you just won't see the password change page after you log in - you'll have to navigate to the admin user's configuration page or use the "person" icon in the top right corner to change the default password to something else.