Go to General Ledger from the main menu. Choose all under List Transactions. Find the shipments you want to reverse. Note that for each order item that is shipped, a GL transaction is posted. Filter by the Transaction Type of Order Shipment and use the date range filter to find the records you want to reverse. Then click on the reverse link next to each row to reverse the transaction. Leave the reversal date blank if you just want use date from the transactions being reversed.