If you want to override the Yoast default category to get the full category path of a product in the "product_type" attribute.

wppfm_product_category_string_gets_full_category_path.php

<?php

function wppfm_product_category_string_gets_full_category_path( $data, $feed_id, $product_id ) {
     $data['product_type'] = WPPFM_Taxonomies::get_shop_categories( $product_id, ' > ' );
 
     // Always return data!
     return $data;
 
}
 
add_filter( 'wppfm_feed_item_value', 'wppfm_product_category_string_gets_full_category_path', 10, 3 );

If you’re unfamiliar with filters in your wp-admin, the best and easiest way to do this is by using a plugin like “Code Snippets” (https://wordpress.org/plugins/code-snippets/). And here you can find a great video explaining the use of this plugin https://www.youtube.com/watch?v=I1_ZqnQmwJs.
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​After activating the Code Snippets plugin you can use the code to add the functionality.