When an item(s) are not available to complete the order and you receive a RED box indicating there is no stock on the item, you are able to pull the units off of the original order and SPLIT it to a new DRAFT order. You will receive an Error message which will not allow you to move forward with your order and give you some options.
You will need to select an option or else it will not allow you to move forward.
Once you successfully Split the item(s), you will create a new DRAFT order which you can find in MY ORDERS and you can complete that order. (Due to this order being a draft order, it will not automatically ship on its own. You will still need to complete the order and submit it.)