Hello!
By default you can only remove member from the chat and it may helps only if it is private talk. If the user has access to the page with messenger block, then this member can be joined automatically when post one message.
We will add new options to the nearest update with these abilities:
https://github.com/unaio/jot-client-una/issues/67
https://github.com/unaio/jot-client-una/issues/66
https://github.com/unaio/jot-client-una/issues/65

and also new privacy groups for profiles who can contact with the profile.