The admin password can be added to the GameUserSettings.ini which can be edited from the config section of my.gameservers.com. Alternatively, this file can be found in the arkse/ShooterGame/Saved/Config/WindowsServer directory of your ftp.
1. Load the GameUserSettings.ini
2. Scroll down to [ServerSettings] (New servers may need to add this to the last line of the .ini file)
3. Add ServerAdminPassword=
4. Save/submit and restart the server
You should be able to use cheat commands by accessing console (Tab Key) and logging in as admin with the command "enablecheats password"
Once you have logged in, simply issue your desired console command. You can find a list of commands at this steam page: http://steamcommunity.com/sharedfiles/filedetails/?id=454529617&insideModal=1
For other tutorials I recommend checking out this FAQ section: https://my.gameservers.com/faq/index.php?type=GMID&CATID=231