After creating a Subject Group at any time you can re-import data to apply corrections, update data, add data. The import will be keyed on the field selected as the CSV Import Existing Fields Sync Field:

After dragging your data csv into the import box, you can drag any columns in that you would like to add or update.

New Subject ID:

This also allows you to apply a new ID number if for any reason the Student ID on the first import was incorrect (Use the Updated Subject ID Field in the drop down for this). The old ID will be dragged to the subject ID field, the new ID will be dragged into the updates subject ID field:

Validate the Import to identify any errors.

Fatal Errors will need to be corrected in the CSV file.

Once ready Save and you have just updated your Subject Group!