In order to do this, you must be running your BeamMP Server on Lua 5.1. As I am currently writing this, Lua 5.1 is only available to early access members, though I could imagine that the public release will be published shortly.
The file must be in the "Resources/Server" directory and MUST MUST BE NAMED "TZNTools". I currently don't have a way too work around this.
!ban (username) -- Permabans the user
!kick (username) -- kicks the user
... and much, much more to come later