If orders were not completed online you may use order/complete_from_history method to complete orders using history messages:

order/complete_from_history&params={"itemId":<long>,
				    "orders":[uint]}

{
    "completed":<uint>        /* number of completed orders : 
                               1 - one order was completed during request processing; such orders status would be changed to "s":2), 
                               0 - no order was completed during request processing */
}