How to load different content from database when select different option?

I'm developing a mobile app which user have to log in, select a course then select a chapter of the course. My question is how to load different content when going to different courses? The database I used here is phpmyadmin. The details are explained below.

Courses.cs

Attached in CourseList. To link the courses registered under the user based on the username then instantiate the button's prefab based on the courses. A method to activate the content scene(game object) is set in the btn.onClick.AddListener.

 public class Courses : MonoBehaviour
 {
     Action<string> _createCoursesCallback;
 
     // Start is called before the first frame update
     void Start()
     {
         // Define callback
         _createCoursesCallback = (jsonArrayString) =>
         {
             StartCoroutine(CreateCoursesRoutine(jsonArrayString));
         };
 
         CreateCourses();
     }
 
     public void CreateCourses()
     {
         string username = Main.Instance.UserInfo.username;
         StartCoroutine(Main.Instance.Web.GetCourseCode(username, _createCoursesCallback));
     }
 
     IEnumerator CreateCoursesRoutine(string jsonArrayString)
     {
         // Parsing json array string as an array
         JSONArray jsonArray = JSON.Parse(jsonArrayString) as JSONArray;
 
         for (int i = 0; i < jsonArray.Count; i++)
         {
             // Create local variables
             bool isDone = false; // are we done downloading?
             string courseCode = jsonArray[i].AsObject["coursename"]; // key to get value
             JSONObject courseInfoJson = new JSONObject();
 
             // Create a callback to get the information from WebRequest.cs
             Action<string> getCourseInfoCallback = (courseInfo) =>
             {
                 isDone = true;
                 JSONArray tempArray = JSON.Parse(courseInfo) as JSONArray;
                 courseInfoJson = tempArray[0].AsObject;
             };
 
             StartCoroutine(Main.Instance.Web.GetCourse(courseCode, getCourseInfoCallback));
 
             // Wait until the callback is called from WEB (info finished downloading)
             yield return new WaitUntil(() => isDone == true);
 
             // Instantiate Gameobject (item prefab)
             GameObject course = Instantiate(Resources.Load("Prefabs/Button_courses") as GameObject);
             course.transform.SetParent(this.transform);
             course.transform.localScale = Vector3.one;
             course.transform.localPosition = Vector3.zero;
 
             // Fill Information***
             course.transform.Find("Text").GetComponent<Text>().text = courseInfoJson["coursename"];
 
             // Set Button
             Button btn = course.GetComponent<Button>();
             String courseN = courseInfoJson["coursename"];
             
             btn.onClick.AddListener(() =>
             {    
                 Main.Instance.CourseContent.SetActive(true);
                 StartCoroutine(Main.Instance.Web.EnterCourse(courseN));
             });
 
             // Continue to the next course
         }
     }
 }

Contents.cs Attached in ChapterList. To link the content registered under the course based on the course then instantiate the image's prefab based on the content in the database.

 public class Contents : MonoBehaviour
 {
     Action<string> _createContentCallback;
     string course;

     // Start is called before the first frame update
     private void Start()
     {
         
         // Define callback
         _createContentCallback = (jsonArrayString) =>
         {
             StartCoroutine(CreateContentRoutine(jsonArrayString));
         };
 
         CreateContent();
     }
 
     public void CreateContent()
     {
         course = Main.Instance.UserInfo.course;
         StartCoroutine(Main.Instance.Web.GetChapter(course, _createContentCallback));
     }
 
     IEnumerator CreateContentRoutine(string jsonArrayString)
     {
         // Parsing json array string as an array
         JSONArray jsonArray = JSON.Parse(jsonArrayString) as JSONArray;
 
         for (int i = 0; i < jsonArray.Count; i++)
         {
             // Create local variables
             bool isDone = false; // are we done downloading?
             string chapter = jsonArray[i].AsObject["coursechapter"]; // key to get value
             JSONObject contentJson = new JSONObject();
 
             // Create a callback to get the information from WebRequest.cs
             Action<string> getContentCallback = (contentInfo) =>
             {
                 isDone = true;
                 JSONArray tempArray = JSON.Parse(contentInfo) as JSONArray;
                 contentJson = tempArray[0].AsObject;
             };
 
             StartCoroutine(Main.Instance.Web.GetContent(chapter, getContentCallback));
 
             // Wait until the callback is called from WEB (info finished downloading)
             yield return new WaitUntil(() => isDone == true);
 
             // Instantiate Gameobject (item prefab)
             GameObject chapterBox = Instantiate(Resources.Load("Prefabs/Image_chapter") as GameObject);
             chapterBox.transform.SetParent(this.transform);
             chapterBox.transform.localScale = Vector3.one;
             chapterBox.transform.localPosition = Vector3.zero;
 
             // Fill Information***
             chapterBox.transform.Find("Text_name").GetComponent<Text>().text = contentJson["coursechapter"];
             chapterBox.transform.Find("Button_image").transform.Find("Text_image").GetComponent<Text>().text = contentJson["fileimage"];
             chapterBox.transform.Find("Button_video").transform.Find("Text_video").GetComponent<Text>().text = contentJson["filevideo"];
             chapterBox.transform.Find("Button_3dmodel").transform.Find("Text_3dmodel").GetComponent<Text>().text = contentJson["file3d"];
 
             // Continue to the next course
         }
     }
 }

The Hierarchy

So, when I click into a course, the scripts above can show the content well according to the database. But if I back to the course menu and go to another course, the content shown belongs to the previous course selected. It may because of the data only be loaded once in the start method.

Therefore, how to load different content when I go to different courses.