I believe the original poster and many others (including myself) are trying to assign multiple transactions at a time in DESKTOP.  The Batch Actions in the desktop version only include:  Add/Approve and Ignore.  We don't have 'Modify Selected' that the online version apparently has.  Just converting to Quickbooks Desktop and it has been very painful with having to assign thousands of transactions.  Insane the software doesn't allow for a sleeker method of assignment during the transaction review process.