Starting from version 1.20.0, FiboSearch Pro is integrated with the Product Specifications for Woocommerce by Am!n A.Rezapour plugin.
To enable searching in custom tabs, go to WooCommerce → FiboSearch → Search config (tab) → Product search scope → select the “[Product Specifications for Woocommerce] Specifications content” in the “Search in custom fields” section:
Save the settings. After the index is rebuilt, you’ll be able to search in custom tabs.