The comment / remark is a default field that shows on the Abstracts Assigned page.
Usual problem of the comment box not showing is because the advance feature is turned ON called
Use Reviewer Comments in 1.02 Abstract Settings - Reviewing tab: https://www.screencast.com/t/NOG3UtkhIH
(This option allows reviewers to leave private comments/review amongst themselves)
Once this is option is turned OFF. It will display the comment / remark box:
If you have any further questions please do not hesitate to submit a request.