How to move my GameObject to desired position?

Question

My math skills have once again come to haunt me. I am building a vertical platformer for mobile devices where the character jumps up onto platforms, trying to get as high as possible while avoiding hazards. I have it set up so that the camera doesn't move, instead the platforms and the character move downwards every time a collision happens between the character and a platform. I cannot figure out how to move the platform that is currently being collided with and the player down to the target location which is -4.0 on the Y-axis in the Main Camera GameObject. Here is the code I have to move the character/platforms down to the target position:

/*********************************** Update **********************************/

void Update(){
    if (platformMove == true) {
        PositionChanging ();

        StartCoroutine(WaitToMove());
    }

}

/******************** Platform Holder Position Changing **********************/

void PositionChanging(){
    Vector2 positionA = new Vector2 (platformHolder.transform.position.x, -4);

    newPosition = positionA;        

    platformHolder.transform.position = Vector2.Lerp(platformHolder.transform.position, newPosition, Time.deltaTime * smooth);
}

//************************ Collision Function ********************************/

void OnCollisionEnter2D(Collision2D coll)
    {
        foreach(ContactPoint2D contact in coll.contacts)
        {   
            platformMove = true;
            currentPlatformPosition = (coll.transform.position.y);

            }
        }
    }

//********************** Wait to Set platformMove to false *******************/

    IEnumerator WaitToMove(){
        yield return new WaitForSeconds(0.5f);
        platformMove = false;
    }

As you can see I am assigning the current collision position to the currentPlatformPosition in the OnCollision2D function but I haven't done anything with it yet. I pretty sure I should be using it somewhere! I've tried a million different things and got close a few times but I can't seem to nail this down.

When platforms are instantiated they are placed inside of the Platform_Holder GameObject. My main character is also in there so he moves with the platforms when I re-position Platform_Holder.

Here is a visual representation:

Answer 1

void Update(){
    if (platformMove == true) {
        PositionChanging ();
    }

}

void PositionChanging(){
    StartCoroutine(WaitToMove());
    Vector2 positionA = new Vector2 (platformHolder.transform.position.x, platformHolder.transform.position.y - 4);

    newPosition = positionA;        

    platformHolder.transform.position = Vector2.Lerp(platformHolder.transform.position, newPosition, Time.deltaTime * smooth);
}

void OnCollisionEnter2D(Collision2D coll)
    {
        foreach(ContactPoint2D contact in coll.contacts)
        {   
            platformMove = true;
            currentPlatformPosition = (coll.transform.position.y);
        }
    }
    IEnumerator WaitToMove(){
        yield return new WaitForSeconds(0.5f);
        platformMove = false;
    }

What I did: 1) Moved your routine call into the method and outside of the loop so that it isn't being continuously called while the platform is moving 2) Changed the hard -4 to the actual y position minus 4 3) Removed an extra bracket (accident?)