unity gameobject findwithtag in project tab??

hello guys im a student in south korea. i have a problem with progressing my project

i changed tag of prefab through script. after i want to using prefab which has certain tag in scene through 'Instantiate' and 'GameObject.FindWithTag', But it doesn't work.....OTL

GameObject.FindGameObjectWithTag ("ShowCard"), ShowCard.transform.position, ShowCard.transform.rotation

i think this problem cause of 'Gameobject.FindWithTag'. it only find gameobject in Hierarchy Tab. so, Is there some solution to observe tag of prefab in PROJECT TAB?