Unable to fulfill some of the items in the order
If you have partially fulfilled some products in the order but you are not able to fulfill the remaining products, you will need to cancel the entire order.
You may refer to this guide on how to cancel an order.
Note: Shopify does not support partial cancellations. As a result, if you cancel an order, all products within the order will be cancelled and the entire order will be refunded back to the customer.