Replying to Attendee chats during a webinar is simple.
When someone sends a message in the chat, you'll see a little red circle appear next to the chat icon in the top right.
Clicking the icon will open the chat, and you'll see the chat messages.
If you hover over the chat message, you'll see the time at which it was sent, as well as a 'Reply' option.
Clicking 'Reply' will make their name appear in your chat box.
This means that your response will only be shown to that Attendee.
After sending the message, it will also show you that the message was a response.
The Attendee will also see that it was a response to them.