add_action( 'wpcf7_init', 'wpcf7_add_form_tag_orderno' );
function wpcf7_add_form_tag_orderno() {
    wpcf7_add_form_tag( array( 'orderno', 'orderno*' ),
        'wpcf7_orderno_form_tag_handler', array()
    );
}
function wpcf7_orderno_form_tag_handler( $tag ) {

    $customer_orders = get_posts( apply_filters( 'woocommerce_my_account_my_orders_query', array(
        'numberposts' => $order_count,
        'meta_key'    => '_customer_user',
        'meta_value'  => get_current_user_id(),
        'post_type'   => wc_get_order_types( 'view-orders' ),
        'post_status' => array_keys( wc_get_order_statuses() ),
    ) ) );

    if ( $customer_orders ) {
        $atts = array();
        $atts['class'] = $tag->get_class_option( $class );
        $atts['id'] = $tag->get_id_option();
        $atts['tabindex'] = $tag->get_option( 'tabindex', 'int', true );
        $atts['name'] = $tag->name;
        $atts = wpcf7_format_atts( $atts );
        echo '<select name="orderno">';
        echo '<option>'.__( "Numéro de la commande", "sinope" ).'</option>';
        foreach ( $customer_orders as $customer_order ) {
            $order      = wc_get_order( $customer_order );
            $item_count = $order->get_item_count();
            echo '
                <option value="'.$order->get_order_number().'">'.$order->get_order_number().'</option>
            ';
        }
        echo '</select>';
    }
}