How to bulk assign orders to pre-generated ground schedule shipments

Hi,

I have successfully generated a series of shipments though grouns schedule and now I need to know the process to plan or assign multiple orders into my newly created shipments and no 1 by 1.
I tried using the bulk plan but it only created new shipments and ignored the previously created ones
Can anyone tell me How can this be done?

P.S.: I have also successfully moved an order to an existing shipment, but as I said I need this done to +1000 orders though a single process (much like the Bulk Plan)

Thanks!!