Canvas makes it easy to reply to messages from other users in your Conversations Inbox.
If you want to reply to a submission comment, you can reply using submission comments in your Inbox or directly from your assignment or quiz.
Click the Conversation you want to respond to . Hover over the timestamp and click the Reply icon  within the message or the Reply icon in the toolbar .
Note: If there is more than one recipient, you can reply-all to the conversation and everyone included will see your reply.
Reply to Message
Type your reply in the message field . You can attach a file or media . When you are ready, click the Send button .
View Sent Message
Your message appears in the preview text of the conversation  and at the top of the individual thread .