Warning users with Cosmobot
You can warn users by replying to a message in the group chat with the warn command - #warn or #w. This will issue a warning to the message sender. The user will be auto-banned in the chat (not globally) after receiving 3 warnings.
Optionally a reason can be specified with the command.
#warn offensive language
To undo the warning use #unwarn or #uw command by replying to a message of the user.
#unwarn
To clear all warnings use #clearwarn or #cw command by replying to a message of the user.
#clearwarn
After a user is auto-banned #unwarn or #clearwarn won't unban them - an explicit unban action is required.
See this to learn how to unban with Cosmobot.