PTO config item in sales order is not able to update

Summary:

We are sending PTO config item -sales order to external system where customer chose either service item or Hardware Item.

After selection, same message has been send to Order Management cloud.

We are not able to add addition Item in existing PTO item in sales order.

How to update existing PTO item with additional config and also update the sales order for the same

Please share resolution for the same

Content (please ensure you mask any confidential information):

We are sending PTO config item -sales order to external system where customer chose either service item or Hardware Item.

After selection, same message has been send to Order Management cloud.