URGENT Recalculate all completed orders cron - Woocommerce

I need help to create a cron job. I need to recalculate tax on all completed orders. Somthing like this. $this->order = new WC_Order($order_id); // Order back to pending $this->order->update_status('pending', '<%Your message%>', TRUE); // Recalculate the order $total = $this->order->calculate_totals(); // Save it, although the calculate also does it. $this->order->save(); IMPORTANT - There is 10.000 orders, and the website cant shut down