On a ticket that came from a chat, you can message the customer directly. The composer has two tabs: Message to reach the customer, and Note for an internal comment only your team sees.
Send a reply
Open the ticket and select the Message tab.
Type your reply. The placeholder reads "Reply to the customer."
Click Send.
Where it goes
Your reply is delivered on the channel the conversation started on, not necessarily the chat widget. A ticket from WhatsApp sends WhatsApp; one from email sends email. Use the Note tab instead when you only want an internal comment.
One side effect
Sending the first message takes the AI agent off that conversation and hands it to your team, so the AI stops auto-answering it.
A manually created ticket has no linked chat, so it has no customer to message; there you can only add notes.