Making a game object move to a specific Vector3 co-ordinate in unity

Question

(I am posting this question because none of the answers provided before worked out for me. Sorry if it sounds like the same question as before.)

I need to switch two cards on click of a button. Although the cards switch with the code I have written, they get swapped so fast. but I need to make them look like moving to each other's location. This is what I have done so far. Now I could move a to b but b is not changing it's position at all.

IEnumerator moveToX(Transform fromPosition, Vector3 toPosition, float duration)
{
    //Make sure there is only one instance of this function running
    if (isMoving)
    {
        yield break; ///exit if this is still running
    }
    isMoving = true;

    float counter = 0;

    //Get the current position of the object to be moved
    Vector3 startPos = fromPosition.position;

    while (counter < duration)
    {
        counter += Time.deltaTime;
        fromPosition.position = Vector3.Lerp(startPos, toPosition, counter / duration);
        yield return null;
    }

    isMoving = false;
}

void swap(string a, string b)
{
    //float step = speed * Time.deltaTime;
    Vector3 temp = GameObject.Find(a).transform.position;
    StartCoroutine(moveToX(GameObject.Find(a).transform, GameObject.Find(b).transform.position, 1.0f));
    //Debug.Log(GameObject.Find(b).transform.position + " => " + temp);
    StartCoroutine(moveToX(GameObject.Find(b).transform, temp, 1.0f));
}

//Button activation(just for testing if swap method worked)
public void ButtonClicked()
{
    swap("Two", "Three");

}