How can i move a game object up and down so it acts like a obstacle for my sphere player

Use the MoveTowards function

 transform.position = Vector3.MoveTowards(firstPosition, endPosition, speed);

https://docs.unity3d.com/ScriptReference/Mathf.PingPong.html

    float speed = 1f;
    float delta = 3f;  //delta is the difference between min y to max y.
 
    void Update() {
         float y = transform.position.y + Mathf.PingPong(speed * Time.time, delta); 
         Vector3 pos = new Vector3(transform.position.x, y, transform.position.z);
         transform.position = pos;
     }

Hey

you can use a Co-Routine and use Vector3.Lerp

 IEnumerator move(Transform _transform)
     {
         startPos = _transform.position;
         t = 0;
 
             endPos = new Vector3(startPos.x + System.Math.Sign(input.x) *  startPos.y = System.Math.Sign(input.y), startPos.z);
         
 
         factor = 1f;
 
         while (t < 1f)
         {
             t += Time.deltaTime * moveSpeed * factor;
             _transform.position = Vector3.Lerp(startPos, endPos, t);
 
             yield return null;
         }
 
         yield return 0;
     }