A comment gets flagged by a student. And only a student can flag a comment.
You will get an email stating a comment has been flagged. In the email you will be provided a link to the page where the comment is.
Also, you can login and navigate to the comment on the “Responses” page.
Once, you are on that page, you can un-flag the comment or hide it from other students until the student who wrote the comment, changes it.