prefabs are not going towards the 'trigger'

I made a script to have prefabs walk towards a 'trigger' but they don't walk towards it and instead they stick to the far left then fall through the floor. I don't know whats happening but i think the prefabs can't detect the 'trigger'. please help

using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.UI;

public class CubeControl : MonoBehaviour {

public Transform target; public float speed; private int current;

public int count; public Text countText; public Text losetext; private Rigidbody rb;

  // Use this for initialization
  void Start()
  {
      rb = GetComponent<Rigidbody>();
      count = 0;
      SetCountText();
      losetext.text = "";
  }
  void OnTriggerEnter(Collider other)
  {
      if (other.GetComponent<Collider>().tag == "trigger")
      {
          Destroy(gameObject);
          count = count + 1;
          SetCountText();
      }
  }
 
  // Update is called once per frame
  void Update()
  {
      // The step size is equal to speed times frame time.
      float step = speed * Time.deltaTime;
 
      // Move our position a step closer to the target.
      transform.position = Vector3.MoveTowards(transform.position, target.position, step);
  }
  void SetCountText()

{ countText.text = "Count: " + count.ToString(); if (count >= 1) { losetext.text = "Game Over!"; }

  } 
  

}