The Class/Department/Location field is not editable on existing Journal Entries created from Revenue Recognition or Amortizations. In order to populate values into these fields for new Journal Entries, the Class, Department or Location should be populated on the source transaction (i.e. Bill, Journal Entry, or Invoice).
Once the Class/Department/Location field has been populated, the new Journal Entries that are generated for Revenue Recognition or Amortization purposes will now contain values on the Class/Department/Location field.
Filling up these fields will not affect existing Journal entries. Currently, the ability to add Class/Department/Location on Revenue Recognition Journal Entry is currently logged under Enhancement 143166.