How can I make sure that the gameObject that collides with the FPSController is the one I need?

I have this script:

     using System.Collections;
     using System.Collections.Generic;
     using UnityEngine;
     using UnityEngine.UI;
     
     public class takeMap : MonoBehaviour
     {
         public int pickUp = 0;
         public GameObject[] items;
         public bool collisionChecker;
         public bool grandPaChecker;
         public bool manChecker;
         public GameObject man;
         public GameObject grandpa;
         public string text2;
         public int score;
         
         
     
         private void Start()
         {
             activateItem(0);
             collisionChecker = false;
             grandPaChecker = false;
             manChecker = false;
         }
     
         private void Update()
         {
             if (Input.GetKeyDown(KeyCode.Alpha1))
                 {
                 activateItem(0);
             }
             else if (Input.GetKeyDown(KeyCode.Alpha2))
             {
                 if (pickUp == 1)
                     activateItem(1);
             }
             else if (Input.GetKeyDown(KeyCode.Alpha3))
             {
                 if(pickUp == 2)
                     activateItem(2);
             }
             else if (Input.GetKeyDown(KeyCode.Alpha4))
             {
                 activateItem(3);
             }
             if (items[1].active == true)
                 if(Input.GetKeyDown(KeyCode.Q))
                     if(collisionChecker = true)
                         if (manChecker == true)
                             {
                         pickUp = 0;
                         activateItem(0);
                         (man.GetComponent(text2) as MonoBehaviour).enabled = false;
                         //progress0 color green
                         Image progressImage = GameObject.Find("progress0").GetComponent<Image>();
                         Color newColor = progressImage.color;
                         newColor = Color.green;
                         progressImage.color = newColor;
                         score++;
            }
             if (items[2].active == true)
                 if(Input.GetKeyDown(KeyCode.Q))
                     if(collisionChecker = true)
                         if (grandPaChecker == true)
                     {
                         pickUp = 0;
                         activateItem(0);
                         (grandpa.GetComponent(text2) as MonoBehaviour).enabled = false;
                         Image progressImage = GameObject.Find("progress1").GetComponent<Image>();
                         Color newColor = progressImage.color;
                         newColor = Color.green;
                         progressImage.color = newColor;
                         score++;
                     }
     
         }
     
         void add(int No)
         {
             pickUp = pickUp + No;
         }
         void activateItem(int itemNo)
         {
             for (int i = 0; i < items.Length; i++)
     
             {
                 items[i].SetActive(false);
             }
             items[itemNo].SetActive(true);
         }
         
         private void OnCollisionEnter(Collision collision)
         {
             collisionChecker = true;
             if (collision.transform.tag == "man")
             {
                 manChecker = true;
             }
             if (collision.transform.tag == "grandpa")
             {
                 grandPaChecker = true;
             }
             
         }
     
         private void OnCollisionExit(Collision collision)
         {
             collisionChecker = false;
             manChecker = false;
             grandPaChecker = false;
         }
     
     }
     

But with this it doesn´t do anything with any object also not with the object which is tagged man. Please help. Regards Crazyplapi.