Login to your Plesk control panel at http://:8080/ and Under Websites and Domains click on the Add New Domain Alias button.
Enter the domain name required for the New Domain Alias into the Domain alias name field and click OK to save.
Note: The domain needs to point to the IP address of your hosting server before these settings will take effect. You can see the IP address of the server on the Websites & Domains page in the control panel.