WordPress Manager is a tool to manage Wordpress installations directly from cPanel without logging into the WordPress dashboard.
By default, WordPress Manager lists installations created through the tool itself. But you can also add manually installed WordPress sites.
To do that, Launch Wordpress Manager from your cPanel and click on 'scan' button
navigate to the 'manual installation' tab, then click on 'start scanning for installations' button
Once the scanning is completed, all your installations will be imported and listed.