Check out example codes for "how to change animator controller in script unity". It will help you in understanding the concepts better.

Code Example 1

//STEP1: Inside the Assets folder, create a new folder called: Resources 
//STEP2: Now Create an Animation folder Inside the Resources folder
//STEP3: Then put the Animator Controller inside this folder (for this examle we'll call the controller Bob)
//STEP4: Now add this to the gamObject that holds the Animator componentAnimator animator;

void Start()
	animator = gameObject.GetComponent<Animator>();

void Update()
    //I put it inside this If Statement to avoid Errors/Warnings but its not 100% necessary
		animator.runtimeAnimatorController = Resources.Load("Animation/Bob") as RuntimeAnimatorController;
        animator.runtimeAnimatorController = Resources.Load<RuntimeAnimatorController>("Animation/Bob");

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