What should I do if it shows this message ? Thank you

You just need to add a RigidBody from the inspector. Click on the object the script is attacked to -> AddComponent -> RigidBody. Another problem could be the missing declaration of the rigidbody in the script. Open the script and paste this.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class MyCass : MonoBehaviour {
    
     private RigidBody _rb;
 
     void Awake()
     {
         _rb = GetComponent<RigidBody>();
     }

On line 9 of your BallControl script, you make sure that AddRelativeTorque is being called on an instance of a Rigidbody component.

you are telling Unity to apply torque in Air ... Unity is a bit angry just make him happy like this

 public Rigidbody rigidbodyReference;
 rigidbodyReference.AddRelativeTorque(Vector3.up * 10);

AddRelativeTorque is a member of Rigidbody class