What is the Primary Device used for reports, and how can I change it?

The Primary Device determines what report set is displayed. You can change the Primary Device by clicking on the Data Sources button and un-selecting devices until the device that you want is labelled ‘Primary Device’.

Here is how the Primary Device is determined:
FreeStyle Libre 3 App
FreeStyle Libre 3 reader
FreeStyle LibreLink App for FreeStyle Libre 2 Sensor
FreeStyle Libre 2 Reader and updated readers
FreeStyle LibreLink App
FreeStyle Libre Reader

Note: Some devices and FreeStyle LibreLink may not be available in your country/region.