add_action('init', 'aovup_register_awaiting_dispatch_order_status');
function aovup_register_awaiting_dispatch_order_status() {
    register_post_status('wc-awaiting-dispatch', array(
        'label'                     => 'Awaiting Dispatch',
        'public'                    => true,
        'exclude_from_search'       => false,
        'show_in_admin_all_list'    => true,
        'show_in_admin_status_list' => true,
        'label_count'               => _n_noop('Awaiting Dispatch <span class="count">(%s)</span>', 'Awaiting Dispatch <span class="count">(%s)</span>')
    ));
}

add_filter('wc_order_statuses', 'aovup_add_awaiting_dispatch_to_order_statuses');
function aovup_add_awaiting_dispatch_to_order_statuses($order_statuses) {
    $order_statuses['wc-awaiting-dispatch'] = 'Awaiting Dispatch';
    return $order_statuses;
}

add_filter('bulk_actions-edit-shop_order', 'aovup_add_awaiting_dispatch_bulk_action');
function aovup_add_awaiting_dispatch_bulk_action($bulk_actions) {
    // Add a new bulk action named "Mark Awaiting Dispatch"
    $bulk_actions['mark_awaiting-dispatch'] = 'Mark Awaiting Dispatch';
    return $bulk_actions;
}

add_filter('handle_bulk_actions-edit-shop_order', 'aovup_handle_mark_awaiting_dispatch_bulk_action', 10, 3);
function aovup_handle_mark_awaiting_dispatch_bulk_action($redirect_to, $doaction, $post_ids) {
    if ($doaction !== 'mark_awaiting-dispatch') {
        return $redirect_to;
    }

    foreach ($post_ids as $post_id) {
        $order = wc_get_order($post_id);
        $order->update_status('awaiting-dispatch');
    }

    $redirect_to = add_query_arg('bulk_awaiting_dispatch_orders', count($post_ids), $redirect_to);
    return $redirect_to;
}