You can customize the associated views Views that are displayed in the forms of other entities. The associated view is different from the views that are visible for the entity in its own area of the user interface. For example, in an account record, under Details, you can click Contacts to view and open a contact form. That is the Contacts associated view. There can be only one associated view of each entity. displayed when you select related records under Details. Most entities have one associated view that is used when the entity is displayed as a related record A record that is referenced in the current record. For example, an account might have many related contact records..
However, the Activity entity has two associated views. To customize the Activity views under Details, you need to know which view is displayed:
The Activities area displays the Open Activity Associated View from the Activity entity.
The History area displays the Closed Activity Associated View from the Activity entity.
You cannot customize the Filter on and Include drop-down lists that limit data in the views. You cannot change the default value or add new values.