How can I block this bot?

I was force-joined to aloha in a slack I was invited to as a guest.

I did NOT opt in to it, and it is pinging me apparently every time I open my laptop and reconnect to slack.

This is not welcome behavior and there seems to be no way to prevent it. The only command it shows is "join" which claims to be opt in. But I did not opt in and I very much want to opt OUT.