How to manage parameters from the main class from different classes (e.g. background)

Hi there:

I'm trying to order my program by putting functions in different files. I've tried with class files, but I run into the following problem:
-When functions where using self.something, it gives an error (it's clear: they are not in the same place anymore).
-When they require components from the main class, I don't have them
-It can't access to the main class features

As an example, I'm trying to access things like view.background from the main class, but no matter how I try, they don't work (the rest, simple functions, do).

If you want to define some functionality for a class in a different file relative to its declaration, you will have to use an extension. Can you provide some code that illustrates the problem you are running into?

Let's say in GameScene.swift file I have a class like this

class GameScene: SKScene {

And from another class in a differenf file:

class backgroundActions: SKSpriteNode {

I want to perform a:

func move(){
scene?.backgroundColor = _

Regarding the previous one, with something like: