NOTE: If you don't configure a mapping that sets the "Assigned to" value in Workbooks, all the imported records will be assigned to you (the individual running the import).

If the records in the CSV import file need to be assigned to different users, ensure the CSV has a suitably named "assign to" column.  This column should contain the user, or queue name, not the user's email address.

Map the "assigned to" in the CSV import file to the "Assigned to" Workbooks field.

If the records in the CSV import file need to be assigned to one particular user, or Unassigned, set up a Fixed Value Mapping Type.  This means you can assign all records to a Fixed Value (this must be a user's name or a queue name) that you set in the mappings screen e.g. You can assign all records to one of your colleagues (use their name), or they can be placed on the Unassigned queue: