Transform not attaching

I'm making a multiplayer game and i have a transform that is the server (wich runs the server scripts), and i'm making a "Reset" key, when i press the key, the player takes the server transform position and teleports to there. My problem is:
I cant attach the server transform to the variable on my script (wich is in the player prefab), when i hit "apply to prefab" it doesn't work.

Sorry for my bad english and thanks in advance.

 

Scene objects cannot be referenced by prefabs
You must populate the variable when the prefab is instantiated in script