Who says it must be blank? If it’s a field in the table you can use it. Telling you not to use the property doesn’t make sense. It is always better to write less code if that option is available.
Are you using the Item Ledger Entry as a DataItem or a record variable? A bit more detail on how you doing what you’re trying to do would help. But as Dhan suggested, if you can’t use the TotalFields property to keep a tally of the “Cost Amount (Actual)” field then CurrReport.CREATETOTALS(“Cost Amount (Actual)”); is the code equivalent. You then have to keep track of your own grouping though. It might be easier to setup the Item Ledger Entry as a DataItem so you can use the properties.