How to change public variable by another script

I'm using Character Controller which sets speed of player. I want to create a script which can stop character after pressing C by setting speed to 0 and set animation named "Sit". After pressing C again, character returns to default animation (standing) and is able to walk. The problem is that I don't know how to change public speed variables from Character Controller using my script and how to set animation that will be active until I press C again.

That's the way I wanted to this.

1. pressing C

2. set animation "Sits"

3. stop by setting speed to 0 (or in another way)

4. pressing C

5. set animation returns to default

6. set speed to default - character is able to moving

   ---

      using UnityEngine;
        using System.Collections;
        
        public class OtherMovements : MonoBehaviour {
        
            bool isSitting = false;
        
            // Update is called once per frame
            void Update () {
    
                if (Input.GetMouseButton(0)) {
                    animation.Play("Attack");        
                }
        
                if (Input.GetKey (KeyCode.C) && isSitting == false) {
                    isSitting = true;
                    transform.animation.Play("Sits");
                    
                }
                if (Input.GetKey (KeyCode.C) && isSitting == true) {
                       isSitting = false;
                       transform.animation.Play("Walk"); 
                    
                }
        
        
            
            }
        }