Trying to start a new flight plan in Sim Brief. The Flight Info section does not provide blocks for either departure or arrival airports?
Can you please provide a screenshot of your issue?
Regards,
Tim
Depart field: ICAO identifier code of departure airport
(not the departure time, as evidenced by the presence of a different input field for departure time to the right of the Arrive field) 
Arrive field: ICAO identifier code of arrival airport
Regards,
Tim