Cannot Send Class Object From One Scene to Another

I’m developing a Unity game. I have a login scene in the game that fetches user information from the database. After fetching the user information, a model class which is named as RegisteredUser is used to hold the user credentials. I need to send the created RegisteredUser class object to the next scene. But I cannot send it directly. When I try it, I get NullExceptionError and the object is lost. How can I fix it? This is the callback function that user credentials are returned:

    public void userInfo (RegisteredUser newUser)
 {
     loggedinUser.FirstName = newUser.FirstName;
     loggedinUser.LastName = newUser.LastName;
     loggedinUser.Email = newUser.Email;
     loggedinUser.Gender = newUser.Gender;
 
 
 }

And this is the part where I want to fetch the name and surname of the user to print on the text field:

  void Start()
 {
   //  string userName = currentUser.FirstName + currentUser.LastName;
     welcomeText = GameObject.Find("Canvas/SidebarPanel/WelcomeText").GetComponent<Text>();
 
 }