If you would like you customers to access your portal at a subdomain (return.yoursite.com) then this can be setup easily.
Open the clicksit return center App
Select customize when when the clicksit return center app is open
Enter the name you would like to have for your custom domain.
Access Advanced DNS settings
Add CNAME record
Set Host as return. And points to: return.clicksit.com
If you have any issue then please don't hesitate to contact us on firstname.lastname@example.org