To find the Grid or Essential Grid plugin, first navigate to WP Admin > X > Validation page (see screenshot)
Once you're on the validations page, scroll down a bit and find the Extensions sections (see screenshot)
Here you'll find the list of extensions that you can install on your site. Find The Grid plugin or the Essential Grid plugin and install it.
To learn more about Addons, please see https://theme.co/apex/forum/t/addons-extensions/78
To use these extensions in X I'd recommend you to please check out these articles as well:
Hope this helps!