Problem with repeating function

using UnityEngine;
using System.Collections;

public class ja : MonoBehaviour {

    // Update is called once per frame
	void Update()
	{
		if (Input.GetMouseButtonDown (0)) {

			GetComponent<Rigidbody2D>().gravityScale = 0.8f;
		}
	}

	void OnTriggerEnter2D(Collider2D col)
	{
		Debug.Log ("Collision!");
		
		if (col.gameObject.tag == "vracanje") 
		{
			transform.position = new Vector3(0, 12,15);
		} 
	}
}

Here I have an object and when I press button it starts falling.
And when my ball hit a ground it appear again on first position, but after that my ball start falling without pressing a mouse button, so I want reset that function in “void update”
Thank you
If you something do not understand, i Will try to describe again.

When you reset the position back to the top, the gravityScale that you set is still 0.8, so the object is still subject to gravity and will continue to fall. So at the same time you change the position, set the gravityScale back to 0 and you should be good to go.