How do I make a 3D Rigidbody move along a path indefinitely?

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.AI;
 public class Test : MonoBehaviour
 {
     public Transform[] Destinations;
     public NavMeshAgent agent;
 
     void FixedUpdate()
     {
         for (int i = 0; i < Destinations.Length;)
         {
          agent.SetDestination(Destinations[i].position);
          if(agent.transform.position.x == Destinations[i].position.x)i++;
         }
     }   
   

use NavMeshAgent Instead