Question Starting / Ending the game on pressing the A button

I have a program that runs in update and It needs to since I need data every frame however, I would like to start / stop the generation when I push the A button on my Quest 2 controller. This will make it easier to collect the data. I've attached the code that I am currently using. I am having a few more issues and I've posted separate help requests:
https://forum.unity.com/threads/permanently-instantiate.1226139/

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using System.IO;
5. using UnityEngine.XR;
6. public class TrackAllPositions : MonoBehaviour
7. {
8.     public GameObject CenterEyeAnchor;
9.     public GameObject RightControllerAnchor;
10.     public GameObject LeftControllerAnchor;
11.     public Transform TrackerCube;
12.  
13.  
14.     // Start is called before the first frame update
15.     void Start()
16.     {
17.         // var headPosition = CenterEyeAnchor.transform.position;
18.         var headX = CenterEyeAnchor.transform.position.x;
19.         var headY = CenterEyeAnchor.transform.position.y;
20.         var headZ = CenterEyeAnchor.transform.position.z;
21.  
22.         //var handRPosition = RightControllerAnchor.transform.position;
23.         var handRX = RightControllerAnchor.transform.position.x;
24.         var handRY = RightControllerAnchor.transform.position.y;
25.         var handRZ = RightControllerAnchor.transform.position.z;
26.  
27.  
28.  
29.         //var handLPosition = LeftControllerAnchor.transform.position;
30.         var handLX = LeftControllerAnchor.transform.position.x;
31.         var handLY = LeftControllerAnchor.transform.position.y;
32.         var handLZ = LeftControllerAnchor.transform.position.z;
33.  
34.  
35.         float centroidX1 = (handRX + handLX + headX);
36.         float centroidX = centroidX1 / 3;
37.  
38.         float centroidY1 = (handRY + handLY + headY);
39.         float centroidY = centroidY1 / 3;
40.  
41.      
42.  
43.  
44.     }
45.  
46.  
47.  
48.     void CreateText()
49.     {
50.  
51.         var headX = CenterEyeAnchor.transform.position.x;
52.         var headY = CenterEyeAnchor.transform.position.y;
53.         var headZ = CenterEyeAnchor.transform.position.z;
54.  
55.         //var handRPosition = RightControllerAnchor.transform.position;
56.         var handRX = RightControllerAnchor.transform.position.x;
57.         var handRY = RightControllerAnchor.transform.position.y;
58.         var handRZ = RightControllerAnchor.transform.position.z;
59.  
60.  
61.  
62.         //var handLPosition = LeftControllerAnchor.transform.position;
63.         var handLX = LeftControllerAnchor.transform.position.x;
64.         var handLY = LeftControllerAnchor.transform.position.y;
65.         var handLZ = LeftControllerAnchor.transform.position.z;
66.  
67.  
68.         float centroidX1 = (handRX + handLX + headX);
69.         float centroidX = centroidX1 / 3;
70.  
71.         float centroidY1 = (handRY + handLY + headY);
72.         float centroidY = centroidY1 / 3;
73.  
74.  
75.         //Path of File
76.         string path = Application.dataPath + "/Log.txt";
77.         //Create File if it doesn't exist
78.         if (!File.Exists(path))
79.         {
80.             File.WriteAllText(path, "Centroid Coordinates in XY on");
81.             File.AppendAllText(path, File.GetCreationTime(path) + "\n\n ");
82.         }
83.  
84.         //Content of file
85.         string content = centroidX + ", " + centroidY + "\n";
86.  
87.         //Add the text
88.         File.AppendAllText(path, content);
89.  
90.      
91.  
92.     }
93.  
94.     // Update is called once per frame
95.     void Update()
96.     {
97.         // var headPosition = CenterEyeAnchor.transform.position;
98.         var headX = CenterEyeAnchor.transform.position.x;
99.         var headY = CenterEyeAnchor.transform.position.y;
100.         var headZ = CenterEyeAnchor.transform.position.z;
101.  
102.         //var handRPosition = RightControllerAnchor.transform.position;
103.         var handRX = RightControllerAnchor.transform.position.x;
104.         var handRY = RightControllerAnchor.transform.position.y;
105.         var handRZ = RightControllerAnchor.transform.position.z;
106.  
107.  
108.  
109.         //var handLPosition = LeftControllerAnchor.transform.position;
110.         var handLX = LeftControllerAnchor.transform.position.x;
111.         var handLY = LeftControllerAnchor.transform.position.y;
112.         var handLZ = LeftControllerAnchor.transform.position.z;
113.  
114.  
115.         float centroidX1 = (handRX + handLX + headX);
116.         float centroidX = centroidX1 / 3;
117.      
118.         float centroidY1 = (handRY + handLY + headY);
119.         float centroidY = centroidY1 / 3;
120.  
121.         float centroidZ1 = (handRZ + handLZ + headZ);
122.         float centroidZ = centroidZ1 / 3;
123.  
124.  
125.         //Debug.Log("Centroid Coordinates in XY Plane = (" + centroidX + ", " + centroidY +")")
126.  
127.         Instantiate(TrackerCube, new Vector3(centroidX, centroidY, centroidZ), Quaternion.identity);
128.  
129.         CreateText();
130.  
131.  
132.      
133.  
134.  
135.  
136.  
137.     }
138.  
139.  
140.  
141.  
142.  
143.  
144.  
145.  
146.  
147. }
148.