The admin of the Facebook page can manage/delete the comments under the ads. To delete unwanted comments, follow the next steps:
Step 1: Go to https://business.facebook.com and on the left side select the page that the campaign is running from.
Step 2: Go to Inbox. If you do not see the 'Inbox' option is because you do not have full admin rights to the page.
Step 3: Select 'Facebook comments'.
Step 4: Click on the three dots next to the comment and select either ‘Delete’ or ‘Hide comment’.