For basic content transfer, You can use the built in WordPress importer. Important: the demo content importer for the premium WPKoi themes could have some compatibility problem with the WordPress importer, so if You want to use it, it is recommended to turn off the demo content feature at the Appearance-> Theme page before.
If You want to transfer the whole site You made to another domain or server, i recommend All-in-One WP Migration plugin.
Add WPKoi designs to Your site with
WPKoi Templates for Elementor plugin