Hello,
On the page you provided, it is shortcode of plugin which is not activated on your site, but was activated on the demo.
If you prefer the Dokan, just edit the page and change the shortcode or you can delete this demo page.
To install the Dokan, go to XStore > Plugins Installer, or install the plugin archive manually.
If you have any additional questions or concerns, please do not hesitate to reach out to us. Our support team is always available to assist you.
Kind Regards,
8theme team