If you have already added a secondary domain to your Deluxe or Ultimate Plesk hosting account, you can change the root folder this domain is using. This will change which folder your secondary domain uses for its websites.
Don't know what kind of hosting you have? You can find that out in your account settings.
If you have already installed an application for this domain, you will not be able to change the domain root folder until the application is removed.
The secondary domain name now points to the new folder. If your website files are in the new folder, your website will display when you navigate to your domain in a web browser.