Here you can update the DXCC lookup data that is used for displaying callsign information.
This data is provided by Clublog.
After updating, Cloudlog can fill in missing callsign information in the logbook using the newly-obtained DXCC data. You can choose to check just the QSOs in the logbook that are missing DXCC metadata or to re-check the entire logbook and update existing metadata as well, in case it has changed.