Custom Meta Data in attribute mapping missing

In my functions.php I added custom fields for my products.

// Custom Product SEO TITLE
    woocommerce_wp_text_input(
        array(
            'id' => '_custom_product_seo_title_terms',
            'placeholder' => 'Custom Product SEO / Feed Title Terms',
            'label' => __('Titel SEO Terms', 'woocommerce'),
            'desc_tip' => 'true',
            'style' => 'max-width:400px;'
        )
    );

In the past I was able to select that custom fields in the “attribute mapping”, after I re-installed my website I am not able to do this anymore.

Did you remove this function? How can I still do this?
I have a lot of products that have better SEO titles in the custom fields, I dont want to update product per product.