You want to know how to change a transaction to an uncommitted status in the Admin Console.
Open the transaction (go to the Transactions tab > pull up the transaction using the filters > click the document code in blue)
Click Edit > choose an Adjustment Reason (drop down menu, right column) > click Save as Uncommitted
Note: Most customers choose to VOID rather than update transactions to Uncommitted, because you can Void several transactions at once on the Transactions tab or using a Transaction Import, see Adjusting Transactions. Voided and Uncommitted transactions are kept out of normal reports and returns filing, which is typically the desired end result of this type of adjustment, so Void works just as well, and is a quicker process.