ARFoundation help needed

I am making Augmented Reality based furniture application. Currently the issue that i am facing is my object is floating after placing.
Secondly i want to stop my plane detection after I place an object and if i have to resume again what should i do?
Lastly I want to ask how I reset my session so all planes and objects get removed.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.XR.ARFoundation;
5. using UnityEngine.Experimental.XR;
6. using System;
7. public class ARTapToPlaceObject : MonoBehaviour
8. {
9.     public GameObject objectToPlace;
10.     public GameObject placementIndicator;
11.  
12.     private ARSessionOrigin arOrigin;
13.     private Pose placementPose;
14.     private bool placementPoseIsValid = false;
15.     private bool placementIsComplete = false;
16.     void Start()
17.     {
18.         arOrigin = FindObjectOfType<ARSessionOrigin>();
19.     }
20.     void Update()
21.     {
22.         UpdatePlacementPose();
23.         UpdatePlacementIndicator();
24.         if (placementPoseIsValid && Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Began)
25.         {
26.             PlaceObject();
27.         }
28.     }
29.     private void PlaceObject()
30.     {
31.         placementIsComplete = true;
32.         Instantiate(objectToPlace, placementPose.position, placementPose.rotation);
33.  
34.      
35.     }
36.     private void UpdatePlacementIndicator()
37.     {
38.         if (!placementIsComplete && placementPoseIsValid)
39.         {
40.             placementIndicator.SetActive(true);
41.             placementIndicator.transform.SetPositionAndRotation(placementPose.position, placementPose.rotation);
42.         }
43.         else
44.         {
45.             placementIndicator.SetActive(false);
46.         }
47.     }
48.     private void UpdatePlacementPose()
49.     {
50.         var screenCenter = Camera.current.ViewportToScreenPoint(new Vector3(0.5f, 0.5f));
51.         var hits = new List<ARRaycastHit>();
52.         arOrigin.Raycast(screenCenter, hits, TrackableType.Planes);
53.         placementPoseIsValid = hits.Count > 0;
54.         if (placementPoseIsValid)
55.         {
56.             placementPose = hits[0].pose;
57.             var cameraForward = Camera.current.transform.forward;
58.             var cameraBearing = new Vector3(cameraForward.x, 0, cameraForward.z).normalized;
59.             placementPose.rotation = Quaternion.LookRotation(cameraBearing);
60.         }
61.     }
62. }