get my scripts to talk to each other

I am struggling to access a custom script from the standard asset AICharacterController, the script is attached to an empty game object that I am using as a game manager. I have edited the AI script to access my manager object but I am unable to get the component script that I have made. Could this be a namespace issue? anyway here is my code : ) thanks

 using System;
 using UnityEngine;
 
 namespace UnityStandardAssets.Characters.ThirdPerson
 {
     [RequireComponent(typeof(UnityEngine.AI.NavMeshAgent))]
     [RequireComponent(typeof(ThirdPersonCharacter))]
 
     public class AICharacterControl : MonoBehaviour
     {
         public UnityEngine.AI.NavMeshAgent agent { get; private set; }
         public ThirdPersonCharacter character { get; private set; }
         public Transform target;
         Animator animator;
 
         public GameObject gameManager;
         public GameObject player;
         Component managerScript;
 
         private void Start()
         {
             agent = GetComponentInChildren<UnityEngine.AI.NavMeshAgent>();
             character = GetComponent<ThirdPersonCharacter>();
             animator = GetComponent<Animator>();
 
             gameManager = GameObject.Find("GameController");
             managerScript = GetComponent<PlayerManager>(); //This should find the script attatched to the game object
             player = GameObject.Find("Player");
 
 
             agent.updateRotation = false;
             agent.updatePosition = true;
 
             SetTarget(player.transform);
         }
 
 
         private void Update()
         {
             if (animator.GetBool("Dead"))
                 SetTarget(agent.transform);
 
             managerScript.TakeDamage(1); //this should edit the health
 
             if (target != null)
                 agent.SetDestination(target.position);
 
             if (agent.remainingDistance > agent.stoppingDistance)
                 character.Move(agent.desiredVelocity, false, false);
             else
                 character.Move(Vector3.zero, false, false);
         }
 
 
         public void SetTarget(Transform target)
         {
             this.target = target;
         }
     }
 }

.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 
 public class PlayerManager : MonoBehaviour
 {
     public GameObject player;
     public float maxHealth = 100;
     float currentHealth;
     bool alive = true;
     bool dead = false;
     public Camera cam1;
     public Camera cam2;
 
     // Start is called before the first frame update
     void Start()
     {
         cam1.enabled = true;
         cam2.enabled = false;
         currentHealth = maxHealth;
     }
 
     // Update is called once per frame
     void Update()
     {
         if (Input.GetKeyDown("9"))
             currentHealth -= 100;
 
 
         if (currentHealth <= 0)
         {
             alive = false;
         }
 
         if (!alive && !dead)
         {
             Die();
         }
     }
 
     public void TakeDamage(float ammount)
     {
         currentHealth -= ammount;
     }
 
     private void Die()
     {
         SwitchCam();
         player.transform.position = new Vector3(170, 10, -220);
         dead = true;
     }
 
     private void SwitchCam()
     {
         cam1.enabled = !cam1.enabled;
         cam2.enabled = !cam2.enabled;
     }
 
     public bool IsDead()
     {
         return !alive;
     }
 }
 
 

I have commented the lines that have issues