Hello, @riwazweb,
Yes, you have to reset and start from scratch. Please read our theme documentation about the theme Install and Demo import here: https://xstore.helpscoutdocs.com/category/8-theme-installation
And please watch the video here: https://www.youtube.com/watch?v=4n1re0jKorc&list=PLMqMSqDgPNmCCyem_z9l2ZJ1owQUaFCE3&index=1
It is recommended to run import on a fresh WordPress installation. For this you can use the WordPress Database Reset plugin https://wordpress.org/plugins/wordpress-database-reset/ The plugin can be used to remove all the existing content and install a new version from scratch.
Importing multiple demos on the same site always overrides and duplicate the content and makes your site glitch.
Regards 8Themes Team.