Try one of the following:
- Search your dashboard for a site using the domain name. You can enter the URL in the search field to search.
- If an old site was using the domain, locate it and unset the domain, then republish.
- Contact the owner if you know who owns the domain or who might have set it up.
- Login to your domain host and create a TXT record with the name value domainverification and have its text value be proofofdomainXX-XX-XX (the XX-XX-XX is today's date). This demonstrate that the domain's owner (you) is requesting the change.