To adjust the URL Settings, first click 'publish' in the editor screen:

Then select 'Smart PDF'

You will find the URL options at the top of this screen:

There are two URL settings:

If you have configured a custom domain name, you can select that via this drop-down menu.

If you want to change the wording of the URL you can do that via this box:

If you make any changes to the URL Settings you will need to click either the 'Publish' or the 'Update' button at the bottom of the screen to save the changes: