I can not save update dropdown count on prefab.

4693220--442745--upload_2019-6-28_12-6-8.png

sorry i done

You are trying to replace or create a Prefab from the instance ‘Item’ that references a missing script. This is not allowed.
Please change the script or remove it from the GameObject.
UnityEditorInternal.InternalEditorUtility:ProjectWindowDrag(HierarchyProperty, Boolean)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)