@JFay 

For product fees you can’t select specific products, you only have the option to select collections/categories. But there is workaround for this.. you can create a specific collection/category on your store, name it something like feed category and use this for the feed you want to create. And in that category on your store back-end add the products that you want. You don’t need to publish this category on your website, just have it on the back end for this purpose I guess.

If you’re using Shopify you can also include/exclude based on product tags!
 

So if there are only one or two specific products you want to include / exclude and don’t want to create additional collections just tag them in Shopify.