Already made flight plans

Hi, I thought it is simple to add fllight plan already done. I have read manuels and instructions but still am trying to learn. I try to install flight plan for one of venice airports using latest version of ttools but I get message that aiport is not in list and there is an error. Can someone help with which steps to use to install? I really don't want to install any of the so called quick ai helplers because I have visited websites and read and they seem to be headache. I know I lack brain source power right now so please be patient with me while I trudge throuhg this. Thank yu much, jakob 
