Make sure you are in game on your server to complete this:
Log in as Admin through your in game console commands by pressing tab.
(To login as admin on your server in game, press tab and enter this: enablecheats <yourserveradminpasswordgoeshere> and press enter.)
After you have successfully signed in as admin, bring up the console again by pressing tab again and enter this: admincheat BanPlayer <Steam ID>
In the < > you will need to enter the person you desire to ban Steam ID. This will ban them from your server and if they are in game at that time, it will kick them first as well.
( Helpful Tip/Another way you can do this using Server Admin UI):
Login as admin the same way, after you are admin, press tab again to bring up the console and enter this: ShowMyAdminManager and press enter.
This will bring up a well organized in-game menu which is called the Server Admin UI. The pop up window should look like this:
You will see in the window different options you can edit.
To the left you will see ARK:, there it shows you what you are able to edit in your server.ini.
The middle section shows you all the connected players that are on your server at that current time. It will list their survivor names, levels and Steam name. This is the same section you will use to ban/kick or whitelist someone. ( If you rather do this in the control panel, click HERE to go to our knowledge base article and it will show you how to whitelist a player via the control panel)
The Cheat Manager allows you to run the cheat command of your liking.
( Click HERE and it will take you to our article on more information and detail on how to use Server Admin UI and what all you can do)