Canned responses are messages that are triggered manually using a pre-existing template. You can send them from the conversation on the inbox.
Open the conversation to the guest thread.
Click Canned responses beside the Send button.
Select the name of the message template you want to use.
If needed, you can select additional message templates before sending. You can also edit the contents of your canned responses.
Click here to learn How to Setup a Canned Response