Need help on 2nd domain and webbuilder new sight

I have 2 domains and 2 website builder sights built. I have one site working fine.
But the 2nd sight www.walkaboutjourney.com is giving me the below.
What do I need to do to have this new webbuilder site work with my 2nd domain?

Domain can not be associated to the selected site.

The selected site already has a domain associated to it. WebsiteBuilder supports only 1 domain association for a site at a time. Please disassociate the existing domain and try again.