This video covers how to assign a Smart Account to an order at the header and line item level.
Note: We had a recent requirement to do export check if the SA is assigned after shipment. This will result in few orders not be available for up to 96 hours. Enhancement is planned to be completed by July which will reduce this SLA of 96 hours.
If your order is assigned to an incorrect Customer Smart Account, open a support case to modify the Smart Account assignment.