Duplicate scriptableobject from custom editor window?

I want this to be done NON-Runtime.

I want to duplicate a SO with a button click from a custom window. Is this possible?

 if (GUILayout.Button("Add Item"))
         {
             CreateInstance("CreateItem");
         }

This is what i have in the OnGUI() function. Where "CreateItem" is a scriptable object coming from a GameManager Gameobject's script. This is the only thing in GameManager.cs:

 public class GameManager : MonoBehaviour{
     public ScriptableObject createItem;
 }

And then i drug the SO to that field on the component.