How do I block an User on Wikia?

I was informed par a user on the Monster Buster Club Wikia, that a user was insulting other users and doing vandalism around that Wikia and on a jour I became a Admin there (Havent logged in there for an half year, so I dont know that). Now I want to block the guy who insulted etc. the other users but it shows this here. I also tried to put like it was a dit on a Wikia page of Help par Blocking to use this "Special:Block".

Can I block him ou do I have to ask it someone of those mentioned Groups?