Moving Maincamera slowly to another position

Hello

I want to move main camera slowly from one point to another point when a button is pressed. This button calls the method which has the code to move the camera.

I have tried using the Lerp method but the camera position is changing so fast that when I click on the button camera directly shifting to a new position. I want the camera to move slowly to a new position.

Below is my code, can anyone please help me with this.

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 using System.Collections;
 using System.Collections.Generic;
 
 using UnityEngine;
 
 public class Cameramove : MonoBehaviour
 {
     public GameObject cam;
     Vector3 moveToPosition;// This is where the camera will move after the start
     float speed = 2f; // this is the speed at which the camera moves
     public void move()
     {
         //Assigning new position to moveTOPosition
         moveToPosition = new Vector3(200f, 400f, -220f);
         float step = speed * Time.deltaTime;
         cam.transform.position = Vector3.Lerp(cam.transform.position, moveToPosition, step);
         
         
     }
     
 }