WC Backorder Split
WC Backorder Split is a free WooCommerce plugin. When a customer buys more of a product than you have in stock, it moves the extra quantity to a new order with the Backordered status. You ship what you have now and the rest when it arrives.
Installation
1. In WordPress, go to Plugins > Add New Plugin.
How splitting works
When the split happens
The Overview page
Go to WPHEKA > Backorder Split. Administrators and shop managers can open it. The page only shows information; there is nothing to set up.
Developer hooks
Add these to your theme's functions.php or a small plugin.
FAQ
Why wasn't my order split?