Rigidbody item pickup problem

Hello so in using the attached script the problem that this script work only while the pick up button is pressed i want it to work on click to pick up and hover and on click to release Any idea?

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 [System.Serializable]
 public class GrabObjectClass
 {
     public bool m_FreezeRotation;
     public float m_PickupRange = 3f;
     public float m_ThrowStrength = 50f;
     public float m_distance = 3f;
     public float m_maxDistanceGrab = 4f;
 }
 
 [System.Serializable]
 public class ItemGrabClass
 {
     public bool m_FreezeRotation;
     public float m_ItemPickupRange = 2f;
     public float m_ItemThrow = 45f;
     public float m_ItemDistance = 1f;
     public float m_ItemMaxGrab = 2.5f;
 }
 
 [System.Serializable]
 public class DoorGrabClass
 {
     public float m_DoorPickupRange = 2f;
     public float m_DoorThrow = 10f;
     public float m_DoorDistance = 2f;
     public float m_DoorMaxGrab = 3f;
 }
 
 [System.Serializable]
 public class TagsClass
 {
     public string m_InteractTag = "Interact";
     public string m_InteractItemsTag = "InteractItem";
     public string m_DoorsTag = "Door";
 }
 
 public class DragRigidbodyUse : MonoBehaviour
 {
 
     public GameObject playerCam;
 
     public string GrabButton = "Grab";
     public string ThrowButton = "Throw";
     public string UseButton = "Use";
     public GrabObjectClass ObjectGrab = new GrabObjectClass();
     public ItemGrabClass ItemGrab = new ItemGrabClass();
     public DoorGrabClass DoorGrab = new DoorGrabClass();
     public TagsClass Tags = new TagsClass();
 
     private float PickupRange = 3f;
     private float ThrowStrength = 50f;
     private float distance = 3f;
     private float maxDistanceGrab = 4f;
 
     private Ray playerAim;
     private GameObject objectHeld;
     private bool isObjectHeld;
     private bool tryPickupObject;
 
     void Start()
     {
         isObjectHeld = false;
         tryPickupObject = false;
         objectHeld = null;
     }
 
     void FixedUpdate()
     {
         if (Input.GetButton(GrabButton))
         {
             if (!isObjectHeld)
             {
                 tryPickObject();
                 tryPickupObject = true;
             }
             else {
                 holdObject();
             }
         }
         else if (isObjectHeld)
         {
             DropObject();
         }
 
         if (Input.GetButton(ThrowButton) && isObjectHeld)
         {
             isObjectHeld = false;
             objectHeld.GetComponent<Rigidbody>().useGravity = true;
             ThrowObject();
         }
 
         if (Input.GetButton(UseButton))
         {
             isObjectHeld = false;
             tryPickObject();
             tryPickupObject = false;
             Use();
         }
     }
 
     private void tryPickObject()
     {
         Ray playerAim = playerCam.GetComponent<Camera>().ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));
         RaycastHit hit;
 
         if (Physics.Raycast(playerAim, out hit, PickupRange))
         {
             objectHeld = hit.collider.gameObject;
             if (hit.collider.tag == Tags.m_InteractTag && tryPickupObject)
             {
                 isObjectHeld = true;
                 objectHeld.GetComponent<Rigidbody>().useGravity = false;
                 if (ObjectGrab.m_FreezeRotation)
                 {
                     objectHeld.GetComponent<Rigidbody>().freezeRotation = true;
                 }
                 if (ObjectGrab.m_FreezeRotation == false)
                 {
                     objectHeld.GetComponent<Rigidbody>().freezeRotation = false;
                 }
                 /**/
                 PickupRange = ObjectGrab.m_PickupRange;
                 ThrowStrength = ObjectGrab.m_ThrowStrength;
                 distance = ObjectGrab.m_distance;
                 maxDistanceGrab = ObjectGrab.m_maxDistanceGrab;
             }
             if (hit.collider.tag == Tags.m_InteractItemsTag && tryPickupObject)
             {
                 isObjectHeld = true;
                 objectHeld.GetComponent<Rigidbody>().useGravity = true;
                 if (ItemGrab.m_FreezeRotation)
                 {
                     objectHeld.GetComponent<Rigidbody>().freezeRotation = true;
                 }
                 if (ItemGrab.m_FreezeRotation == false)
                 {
                     objectHeld.GetComponent<Rigidbody>().freezeRotation = false;
                 }
                 /**/
                 PickupRange = ItemGrab.m_ItemPickupRange;
                 ThrowStrength = ItemGrab.m_ItemThrow;
                 distance = ItemGrab.m_ItemDistance;
                 maxDistanceGrab = ItemGrab.m_ItemMaxGrab;
             }
             if (hit.collider.tag == Tags.m_DoorsTag && tryPickupObject)
             {
                 isObjectHeld = true;
                 objectHeld.GetComponent<Rigidbody>().useGravity = true;
                 objectHeld.GetComponent<Rigidbody>().freezeRotation = false;
                 /**/
                 PickupRange = DoorGrab.m_DoorPickupRange;
                 ThrowStrength = DoorGrab.m_DoorThrow;
                 distance = DoorGrab.m_DoorDistance;
                 maxDistanceGrab = DoorGrab.m_DoorMaxGrab;
             }
         }
     }
 
     private void holdObject()
     {
         Ray playerAim = playerCam.GetComponent<Camera>().ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));
 
         Vector3 nextPos = playerCam.transform.position + playerAim.direction * distance;
         Vector3 currPos = objectHeld.transform.position;
 
         objectHeld.GetComponent<Rigidbody>().velocity = (nextPos - currPos) * 10;
         
         if (Vector3.Distance(objectHeld.transform.position, playerCam.transform.position) > maxDistanceGrab)
         {
             DropObject();
         }
     }
 
     private void DropObject()
     {
         isObjectHeld = false;
         tryPickupObject = false;
         objectHeld.GetComponent<Rigidbody>().useGravity = true;
         objectHeld.GetComponent<Rigidbody>().freezeRotation = false;
         objectHeld = null;
     }
 
     private void ThrowObject()
     {
         objectHeld.GetComponent<Rigidbody>().AddForce(playerCam.transform.forward * ThrowStrength);
         objectHeld.GetComponent<Rigidbody>().freezeRotation = false;
         objectHeld = null;
     }
 
     private void Use()
     {
         objectHeld.SendMessage("UseObject", SendMessageOptions.DontRequireReceiver); //Every script attached to the PickupObject that has a UseObject function will be called.
         objectHeld = null;
     }
 }