"Please enter any comments you would like to send to the Journal Office"
This kind of question is a &quot;catch all&quot; in case there is something you wanted to add that did not fit in any of the other questions in the submission.  If there's nothing you can think of that was not already covered in the rest of the submission, just leave it blank.  I have now submitted a number of papers on submission sites that use a question like this, and I have never had anything to add.