How can I find the prefab asset a child object is belong to ? I want to destroy a child in a prefab

I want to destroy a gameobject that is a child inside a prefab.
But there are also some other prefabs above the child object and then the top prefab asset.

To destroy I need to open the prefab destroy and then close and save the prefab again.

Code (csharp):

1.  
2. if (UnityEditor.PrefabUtility.IsPartOfPrefabInstance(transform))
3.  
4.    UnityEditor.PrefabUtility.UnpackPrefabInstance(gameObject,
5.         UnityEditor.PrefabUnpackMode.Completely,
6.         UnityEditor.InteractionMode.AutomatedAction);
7.  

But instead gameObject how do I know what is the prefab asset ? How do I get the prefab asset if I don't know it's name ?

For example let's say this is my Hierarchy :

PrefabA
GameObjectA
PrefabB
GameObjectB

I want to destroy GameObjectB using DestroyImmediate via code script.
The problem is that in the editor I did already Overrides > Apply Changes on PrefabA
So now GameObjectB is part of the PrefabA and I need by code to open PrefabA DestroyImmediate(GameObjectB) then save the changes to PrefabA

How can I do it ?

It's like doing it in the editor open the PrefabA delete GameObjectB and close the PrefabA
I need ot do it by code in a script in a editor script.