You can find the 32-digit UUID hex number as part of the serial number of the appliances in the footer of the login page. It is also in the footer on the appliance administration pages. If you're setting up a brand new appliance/vm you'll see the serial at the top of the pages of the appliance setup wizard.
The serial number is highlighted below (with a few characters blacked out to protect the innocent).
You can find the 32-digit UUID hex number as part of the serial number of the appliances at the bottom of the appliance registration page.