If this is a charge, where the date does not at all appear, you can copy the expense within the same report. Check the box next to the charge, then click on the Copy button. This will duplicate the expense but as cash. In the copied Cash entry, add the date and then save. In the expense report, you can check off the boxes for both the charge and the cash entry, then click on the Combine button.
If the issue is that the expense came in as a wrong date (due to posting), then you can click on the Itemize link in the expense entry, and itemize all the expense to the same expense type, and change the date in the itemized sub-entry.
