You can add domains or sub-domains to your Managed WordPress account through your Managed WordPress Dashboard.

Go to your TsoHost Client Area account.

Navigate to Services -> My Services -> select the Managed WordPress service -> click on Login to Server

In this control panel, open the Settings tab at the top.

In the Domains section, select Add.

From the pull-down menu, select New Additional Domain.

Select Add Domain to complete the process.

Note: If you're using subdomains, you'll need to also add an "A" record for the new subdomain within the DNS zone of your primary domain.