Kevin,
Unfortunately, this is a known issue / limitation for this feature.
You mention that you want to “Edit” an instance. This is not possible. You cannot edit or delete an instance using the UI. You can edit the event notification and “change” the instance from the one configured to an existing instance.
In order to remove an email "instance", you will need to open a Ciso TAC Case so that they can get assistance from engineering to remove from the database. The Cisco TAC engineer also can attach your SR to the following feature enhancement.
CSCvv85952 - [2.3.x.x] UX - add the ability to delete & clean up Event.Subscription.Endpoints using the UI & API
Also, there is also a limitation of only viewing 10 email instances in Catalyst Center Release 2.3.7.7 and earlier. In Release 2.3.7.9 or later, the view limitation is resolved for email instances.
I hope this helps.
