While site administrators can delete messages and correspondence threads from within the web application they cannot currently delete an an annotation. Admins can only hide annotations, not delete them.

In very rare cases (related primarily to GDPR right to Erasure Cases, or similar cases where we can't justify holding, or don't want to hold, the content of hidden annotations) hiding an annotation is not sufficient, deletion is required.

This probably occurs rarely enough that developer action on rare occasion might be satisfactory, and less effort than actually implementing this. Front-line support admins having this feature would allow quicker case resolution, involving fewer people, and fewer emails though.