Cannot find custom fields in vendors panel

Hi there,
I need to have a custom fields in vendor’s product page.
Using the code below I see the new tab but don’t know where to find this in the product pages (I want to write some text inside, depends on the product features).
I’d like to solve this without a plugin.
See imgs url below.
2 screenshot here:
https://i.stack.imgur.com/PgGNy.png

View post on imgur.com

Thank’s

// Register the Tab by hooking into the 'woocommerce_product_data_tabs' filter
add_filter( 'woocommerce_product_tabs', 'add_my_custom_product_data_tab' );
function add_my_custom_product_data_tab( $product_data_tabs ) {
    $product_data_tabs['my-custom-tab'] = array(
        'label' => __( 'My Custom Tab', 'my_text_domain' ),
        'target' => 'my_custom_product_data',
    );
    return $product_data_tabs;
}

// tab content hooking into the 'woocommerce_product_data_panels' action hook 

add_action( 'woocommerce_product_data_panels', 'add_my_custom_product_data_fields' );
function add_mailchimp_product_data_fields() {
    global $woocommerce, $post;
    ?>
    <div id="my_custom_product_data" class="panel woocommerce_options_panel">
        <?php
        woocommerce_wp_checkbox( array( 
            'id'            => '_my_custom_field', 
            'wrapper_class' => 'show_if_simple', 
            'label'         => __( 'My Custom Field Label', 'my_text_domain' ),
            'description'   => __( 'My Custom Field Description', 'my_text_domain' ),
            'default'       => '0',
            'desc_tip'      => false,
        ) );
        ?>
    </div>
    <?php
}