The short answer - it depends on what import type you are using...
Standard Transaction Import - For this import type you will need to delete the previous file(s) that had errors and reload the corrected file. Importing multiple Standard Transaction Imports may cause duplicate entries, as files are not overwritten.
Standard Manager Investment Activity Import - For this import type you will need to delete the previous files that had errors, and reload the corrected file. Deleting a file will not clear out investment activity. If you need to clear out investment activity, we recommended bringing in a new Manager Investment Activity Import file populated with all zeros for each manger.
Bulk Import - Using this import type you can over-write the existing data and do not have to delete the file with errors.
For questions about the Awards Import and Custom Imports, please contact firstname.lastname@example.org