如何在子主题中添加自定义插件文件？

I have do some customize in /wp-content/plugins/woocommerce/includes/class-wc-download-handler.php, and i want to add it in my child theme . but after i add in to mytheme-child/woocommerce/includes/class-wc-download-handler.php there is nothing changing. May i know how to add the files?

    // Track the download in logs and change remaining/counts.
    $current_user_id = get_current_user_id();
    $ip_address      = WC_Geolocation::get_ip_address();
    if ( ! $download_range['is_range_request'] ) {
        $download->track_download( $current_user_id > 0 ? $current_user_id : null, ! empty( $ip_address ) ? $ip_address : null );
    }

    if (isset($_SERVER["HTTP_REFERER"])) {
        header("Location: " . $_SERVER["HTTP_REFERER"]);
    }

    //self::download( $file_path, $download->get_product_id() );

How to i add this to child theme?