✅ beginner help with unity

Deal: I am trying to take my health float value from a script that is "not" in the scene (just a script) and pass it the child of a Player Gameobject. I have tried to use GetComponent and some basic stuff but i dont know why its not working. I can use GetComponent from my Player object and get the health float but not from the chiöd script.
Any help or advice appreciated!