You can still use the old Send/Replenish workflow in Seller Central to work on or finish shipments created in Boxt.
Content Source on the shipment must be changed to "NONE."
Select the Shipment in Boxt
Select the "edit" icon to edit the shipment:
Change Content Source to NONE, then click the checkmark to save:
When you save that change, you will be asked to Confirm that you which to set content source to NONE. Click Set to NONE.
After you have changed the content source, login to Seller Central
Navigate to Inventory > Shipments:
Locate the desired shipment in the shipping queue and select "Work on Shipment"
You will be presented with the choice of "Return to old workflow" or "Try Send to Amazon." Select "Return to Old Workflow." (Once you select "Try Send to Amazon" for a shipment, the shipment will no longer be able to be modified in Boxt.)
At this point, you are able to modify the shipment, update shipping information, or print shipping labels, etc.