Hello, @Darul Muqarrabin Malaysia,
Actually, It looks like you imported the demo with the one-page builder and tried to edit with another page builder which destroyed your site, and we do not recommend using multiple page builders on the same site at the same time as this caused unexpected issues.
So please reset your WordPress and start from scratch. Please install only a 1-page builder whether “WP Bakery or Elementor” and then import the demo with it. I am sure you will not face this issue anymore. But if yes then please reset the WP completely and let me know I will import the demo for you on your site.
Regards 8Themes Team.