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 to see codes for these  plugins.