From this menu with simple drag and drop you can change the default order of your flights in the "Fleets" menu. You can do this individually for single (1) or Team planet. (2)
Please note, that this rearrangement will affect the view of the fleets menu in your account only. It will not affect by anyway the flights order of other players.
You can easily open this menu from the "Fleets" menu too. Just click the "Rearrange flights" icon next to your Missions drop-down list.