Moving Forward and Backward continously using IENumerator

Hi, I want to make my object move up and down with IENumerator. I'm using this code and my object can move up.

 IEnumerator floatingAround()
     {
         while (isFloat)
         {
             this.transform.position = Vector2.Lerp(this.transform.position, topPosition, Time.deltaTime * speed);
             distance = Vector2.Distance((Vector2)this.transform.position, topPosition);
 
             yield return new WaitForEndOfFrame();
         }

So, I modified it a bit to make my object move down when my object reaches max height, and become like this

 IEnumerator floatingAround()
     {
         Vector2 temp;
 
         while (isFloat)
         {
             if (trigger) temp = topPosition;
             else temp = bottomPosition;
 
             this.transform.position = Vector2.Lerp(this.transform.position, temp, Time.deltaTime * speed);
             distance = Vector2.Distance((Vector2)this.transform.position, temp);
 
             yield return new WaitForEndOfFrame();
         }
        yield return new WaitForEndOfFrame();
 }

but this code won't make my object go down, and its happen too when I try to make my object goes down first. Any suggestion for this code?