Hello,
XStore core plugin is required plugin if you want to use XStore theme and it should be installed and activated. List of required plugins you can find here https://xstore.helpscoutdocs.com/article/36-included-plugins
To install bundled plugins go to Appearance > Install Plugins. Activate installed plugins you can via Plugins > Installed plugins. As I can see Xore plugin is already activated on your site.
Do you need any other help?
Regards
