You can either open a command prompt and navigate to Galciv's steam folder ([STEAMFOLDER]\SteamApps\common\Galactic Civilizations III) and issue the following command "Galciv3 cheat"
or you can create a shortcut that points to the same command
(eg:' "C:\Steam\steamapps\common\Galactic Civilizations III\GalCiv3.exe" cheat ')
and name it something like "Galciv3 Debug" for ease of use. Note that in this case you need to use doublé quotes to enclose the path since it contains spaces,