Most plugins use standard way to store details : table wp_postmeta for order fields and table wp_woocommerce_order_itemmeta for item metas.
So when you click button "Add field" in section "Setup fields" - the plugin shows correct fields/keys and can easily export it.
But some plugins (like Woocommerce Subscriptions) own way for recording details.
In this case - you must add extra code to fetch data.
Please, visit https://algolplus.com/plugins/snippets-plugins/ to see codes for these plugins.