Edit WC shipping method on orders - php

Question

I want to simply change the shipping method of an order on Woocommerce.
I have seen a few posts on editing shipping methods on orders but I'm not 100% clear on the exact protocol of how it works, I have a rough idea but no success yet! If you can help me to get the order to update its shipping method that would be awesome! (this is the middle of a large project so I can't share the whole plugin, let me know if you need anymore details happy to provide anything that's necessary!)
I have this small bit of code that returns me a list of orders that need shipping method updated and the new shipping method rateID that it has to be changed to, that all works fine but i have included it so you can see where it comes from.
Once the array of orders to be updated has been constructed, it then needs to be processed using the set_shipping() method. One at a time working through the array items and updating the shipping method of each, from the original to the new one provided in the toUpdate array
UPDATED: i have tried using the WC_API_Orders() class as set_shipping is a method of that. still coming up with the unrecognised error.
'Class 'Inc\Api\Callbacks\WC_API_Orders' not found'
private function updateRound()
{
if (! empty($_POST['update'])) {
$updateorderID= $_POST['orderID']; //get list of orderID to change
$updateRound= $_POST['newRound']; //list of rounds new orders want swapped to
$updateList= $_POST['update']; //uses a check box to confirm user wants to update row (stops accidentally updating the whole list)
// print_r($_POST['update']); //shows an output to check results.
$toUpdate = []; //this is the array for all the shippingmmethods to update on set order etc.
//make list of order ID's to update and their new shipping method
foreach ($updateList as $key => $value) {
$toUpdate[] = [
'orderID' => $key,
'newRound' => $updateRound[$key]
];
}
}
$absOrder = new WC_API_Orders();
foreach ($toUpdate as $updateOrder) {
//echo "</br>OrderID: ".$updateOrder['orderID']." Round updated to ".$updateOrder['newRound'];
echo "order ".$updateOrder['orderID']."updating";
$absOrder->wc_get_order($updateOrder['orderID']);
echo " order retreived";
$absOrder->set_shipping($order, $updateOrder['newRound'], 'update' );
echo "updated </br>";
}
}
This is for a very local veg delivery scheme, people can only place an order if their postcode is in the set group, so that's not so important, this shipping method we use to change from 'wed round' to 'thurs round' etc. Simple really no concern for delivery companies etc, its all in house. Tax etc. doesn't matter, it's all done elsewhere, this is simply meant to be a way of editing orders onto delivery rounds.