If one or more participants in an event cause feedback or echo through a mic left open, or through poor echo cancellation at their end, then you can stop that via:
- Tell them via private chat/IM somethimg like "I am sorry, you seem to have an open mic, or when your mic is on I am hearing echo. You probably will not hear the problem yourself. So for now I will mute you and will not hear you again in this event".
- Right click on the avatar and select "Mute".
- The avatar will show as "Muted" in their status/group label.
- At the end of the meeting you could unmute them in case they fix the problem for next time.