If you're on Steam, you can't.
His ID is 40k, which implies that he isn't using steam.
To launch a dedicated server, first make a copy of the Blockland shortcut on the desktop. Rename the new one to something you'll remember, like "Blockland Dedicated".
Then, right click on the new shortcut and click properties. In the Target field, scroll all the way to the right of the text, add a space, and then type -dedicated . Then click Apply/OK.
To start your dedicated server, simply double click the new shortcut. It'll load whatever add-on settings were last used in the normal game.
