To edit a Judge's comments, you simply need to pretend to be that judge!
To edit a judge's comments, in your event, navigate to the Judges tab. In the same row as the Judge you want to edit, click “Share Ballot,” then click “View Ballot in New Tab.” This will bring up their ballot.
You can then scroll and find the competitor you want to edit. Type in the box directly to change the comment (or just delete it entirely). It will save automatically. You can confirm this on the Results tab after!