Are you asking if you can modify the record that triggered the Action? Or are you saying that you are saying that a child gets modified or added and you want to modify the Parent.
Either is possible.
The "trick" is to create a Report Link field to identify the records to be edited. When the action asks for related records to be edited in the setup, it in fact does not mean related records. They just use those words. They really mean "the records defined by this report link field.
So you can either modify the record you are on by setting up a Report link field to map from the [Record ID#] right back to the same App, same table and field for the [Record ID#] field or else if this were a case of needing to edit the Parent triggered by an child entry, then make a Report Link field to match [Related Parent] to Record ID# of the Parent.
