This is not possible. Instagram allows for posts to be pulled externally, but it does not allow for a return call. That means that Covet.pics is designed to pull posts from Instagram and make those posts shoppable in Shopify, but not in Instagram. Instagram's API won't allow the transfer of product data.
If you want to tag Shopify products on Instagram, Shopify has a built-in integration with Instagram: www.shopify.com/instagram