Edit the file.
ConanSandbox\Saved\Config\WindowsServer\ServerSettings.ini
MAKE SURE YOUR IN THE CORRECT LOCATION NOT ConanSandbox\Config\WindowsServer\ServerSettings.ini
And add underĀ [ServerSettings]
AdminPassword=SecretPassword
More settings can be found here.
http://steamcommunity.com/sharedfiles/filedetails/?id=853969975