If you are using the  Page Builder plugins to customize your WooCommerce product page, you will need to use the shortcode [fpd] to position FPD, as the hooks that are normally used to position FPD on WooCommerce pages are not accessible.

If you want the designer to open in a lightbox with the button before Add to Cart button, then drag and drop your new text widget there and set your main FPD plugin settings to: