Go to C;// (as i presume you installed default setings) anyways, C://Blockland/Config/server/ and theres a txt file named BANLIST.
Type something like this:
Admin/ID Player/ID Reason Time
"Vaporeon 15634 jolt 17420 -_- -1 -1"
But only the stuff in the quotes.
And Im not sure about the time thing, but thats permaban up there.
Hope it works/helps.
P.S: you can find a players ID on RTB
Just go to add-ons and members, then you can either check the list or click find members.