I wasn’t sure exactly what they were looking for, so I added two sections to my site’s Privacy page:
Data Deletion
Accounts on this site can be anonymized or deleted at the users request. Contact our
@supportgroup for details.App Removal
Any apps authorized for logging users onto the site can be removed by going to the Associated Accounts section of a user’s preferences page.
I configured the headings for these sections as anchor links and then included the anchor for the first section in the URL that I added to the Data Deletion Instructions URL on Facebook (https://forum.example.com/privacy#data-deletion).
It’s not clear to me if Facebook is wanting details about how to remove their app to be displayed, but I don’t think it could hurt to give that information.
At this point, this is my best guess about how to meet Facebook’s criteria. I’ll try to confirm that and update the topic at Configure Facebook login for Discourse soon with details.