How to add Comments to a Feedback Entry?

You can add two different types of comments on a feedback entry:

Just click the "Add comment" button and add up a remark.

A user can add a regular comment as compared to an admin who can also comment confidentially.
Confidential comments will only be visible to your internal teammates and are used to discuss in-between the team. You customers won't be able to see them. 

One can also use @mentioning to mention or reply to a customer or a teammate.