Hello,
Thanks for using our theme.
I do not see demo content on your site. Import the Organic01 version and install the WC Marketplace plugin and you’ll get that demo.
Such feature https://prnt.sc/vnpg6e can be activated via Theme Options > WooCommerce (Shop) > Shop > Products style > Add To Cart With Quantity (Simple Products) > On.
Let us know if you need any further assistance.
Regards