How do I get a pointer to this script from a trigger

So I have a ledge climbing script and I need to get a reference to the ThirdPersonController script that comes with Unity's Start Asset package. But whenever I reference the script from my trigger the compiler will not compile saying it can't find it? Anyone solved this problem or had it? Am I missing something? I've looked all over for an answer and even poured through the code myself but can't figure it out. Thanks for any help in this matter.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Ledge : MonoBehaviour
 {
     [SerializeField]
     private Transform _grabPosition;
     
     private void OnTriggerEnter(Collider other)
     {
         if (other.tag == "LedgeGrab")
         {
             ThirdPersonController player = other.gameObject.GetComponentInParent<ThirdPersonController>();
             
             if (player != null)
             {
                 if (_grabPosition != null)
                 {
                     
                     ThirdPersonController.GrabLedge(_grabPosition.position);
                 }
             }
         }
     }
 }