Canvas makes it easy to reply to messages from other users in your Conversations Inbox.
If your recipient list contains more than 100 users, your message will automatically be sent as individual messages to each user.
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 .