To set countries avoidance for the Flight Time Calculator in Leon go to "Settings" button and access the "Fleet" section. Press "Edit" on the right of the aircraft data. Access "Sales" option and type countries' names in "Exclusion zones". Press "Save" and then "Save and refresh" to apply the list of excluded zones for an aircraft. Please note, the list of "Exclusion zones" should be set for every aircraft separately.
https://aviapages.com/leon/connect/