How can I call a new class function with InvokeRepeating ?

public class CheckInRange{

	public IEnumerator loopCheckInRange(){
		timer += 1;
		Debug.Log (timer);
		yield return new WaitForSeconds (0.2f);
	}
}

In the other class:

public class test : MonoBehaviour {

public CheckInRange checkInrange = new CheckInRange ();
// Use this for initialization
void Start () {
	InvokeRepeating("checkInrange.loopCheckInRange",0f,0.2f);
}

}

That’s not possible InvokeRepeating does only work for methods defined inside the MonoBehaviour where you call the InvokeRepeating on. It can not call methods on some other objects. Even if it would work your code wouldn’t make much sense. You did not create a method but a coroutine. However a yield at the end of the coroutine is completely pointless as the coroutine will wait for the time specified and then it does nothing and just finishes.

It’s impossible to determine your actual goal from your code snippet so we can’t really suggest an alternative without knowing what you actually want to achieve.