A. Check if the app has any updates available that might include new features. Go to the Google Play Store, search for FreeStyle Libre 2, and see if there is an 'Update' button. If there is, update the app and check the settings again for any new customization options.

B. As a workaround, you can change the overall notification sound for the app through your device settings. Go to 'Settings' > 'Apps' > 'FreeStyle Libre 2' > 'Notifications' and see if you can change the notification sound from there.