Heavy Problem on my Food Ordering APP

Hi everyone, I’ve a big problem with databases on Adalo. I’ve created a food ordering app with this logic: I’ve a menu items db, order items db and order db. When the user enter in menù he create an order, then when the user adds menù item into the cart this begins order item. My problem is: when order is complete the cart remains full and if the user cleans the cart, even if the order is complete, the order loses order items. I just thought to create a db called Cart Items as a temporary list of menù items but I don’t know how to copy this list as Order Items when Order is completed. Can you help me?