public list of gameobjects to spawn via AR

Dear C-sharper, I'm quite new in programming.
I'm writing because i'm stuck with a script (using private variables). I simply would like to create a list of gameobject (instead of having only one, like actually is the script) to spawn while tapping the screen. The script is already written. I need to change lines 34/35 and 124 i guess. I tried diverse methods but with any success.  I'm wondering if you can help me to fix the problem. thanks in advance.

I tried:

//public GameObject[] PlacementObjectPf;

NOT WORKING WITH THE LINE 124

Also  public List<GameObject> _placedObjects = new List<GameObject>();

Very best, Chiara

The script:

using System.Collections.Generic;

using Niantic.ARDK.AR;
using Niantic.ARDK.AR.Anchors;
using Niantic.ARDK.AR.ARSessionEventArgs;
using Niantic.ARDK.AR.HitTest;
using Niantic.ARDK.External;
using Niantic.ARDK.Utilities;
using Niantic.ARDK.Utilities.Input.Legacy;
using Niantic.ARDK.Utilities.Logging;

using UnityEngine;

namespace Niantic.ARDKExamples.Helpers
{
  //! A helper class that demonstrates hit tests based on user input
  /// <summary>
  /// A sample class that can be added to a scene and takes user input in the form of a screen touch.
  ///   A hit test is run from that location. If a plane is found, spawn a game object at the
  ///   hit location.
  /// </summary>
  public class ARHitTester: MonoBehaviour
  {
    /// The camera used to render the scene. Used to get the center of the screen.
    public Camera Camera;

    /// The types of hit test results to filter against when performing a hit test.
    [EnumFlagAttribute]
    public ARHitTestResultType HitTestType = ARHitTestResultType.ExistingPlane;

    /// The object we will place when we get a valid hit test result!
    public GameObject PlacementObjectPf;
        //public GameObject[] PlacementObjectPf; NOT WORKING WITH THE LINE 124

        /// A list of placed game objects to be destroyed in the OnDestroy method.
        private List<GameObject> _placedObjects = new List<GameObject>();

    /// Internal reference to the session, used to get the current frame to hit test against.
    private IARSession _session;

    private void Start()
    {
      ARSessionFactory.SessionInitialized += OnAnyARSessionDidInitialize;
    }

    private void OnAnyARSessionDidInitialize(AnyARSessionInitializedArgs args)
    {
      _session = args.Session;
      _session.Deinitialized += OnSessionDeinitialized;
    }

    private void OnSessionDeinitialized(ARSessionDeinitializedArgs args)
    {
      ClearObjects();
    }

    private void OnDestroy()
    {
      ARSessionFactory.SessionInitialized -= OnAnyARSessionDidInitialize;

      _session = null;

      ClearObjects();
    }

    private void ClearObjects()
    {
      foreach (var placedObject in _placedObjects)
      {
        Destroy(placedObject);
      }

      _placedObjects.Clear();
    }

    private void Update()
    {
      if (_session == null)
      {
        return;
      }

      if (PlatformAgnosticInput.touchCount <= 0)
      {
        return;
      }

      var touch = PlatformAgnosticInput.GetTouch(0);
      if (touch.phase == TouchPhase.Began)
      {
        TouchBegan(touch);
      }
    }

    private void TouchBegan(Touch touch)
    {
      var currentFrame = _session.CurrentFrame;
      if (currentFrame == null)
      {
        return;
      }

      var results = currentFrame.HitTest
      (
        Camera.pixelWidth,
        Camera.pixelHeight,
        touch.position,
        HitTestType
      );

      int count = results.Count;
      Debug.Log("Hit test results: " + count);

      if (count <= 0)
        return;

      // Get the closest result
      var result = results[0];

      var hitPosition = result.WorldTransform.ToPosition();

      _placedObjects.Add(Instantiate(PlacementObjectPf, hitPosition, Quaternion.identity));
            
            var anchor = result.Anchor;
      Debug.LogFormat
      (
        "Spawning cube at {0} (anchor: {1})",
        hitPosition.ToString("F4"),
        anchor == null
          ? "none"
          : anchor.AnchorType + " " + anchor.Identifier
      );
    }
  }
}