Error code: Thread 1: EXC_BAD_ACCESS (code=2, address=0x7ffee3239efc)

I am trying to access a label in a viewcontroller from a model class so that I can change the UILabel text every time there is an error, however, every time I create the viewcontroller object inside the model class this error always appear. If i delete the object declaration then everything will work just fine. Can anyone tell me how to solve this problem? Your comment will be highly appreciate!

Model
import Foundation

import Firebase



class SignUp{

    

    let db = Firestore.firestore()

    var emailTextFieldCopy:UITextField!

    var passwordTextFieldCopy:UITextField!

    var fullnameTextFieldCopy:UITextField!

    var usernameCopy:UITextField!

    

    var errorText:String?

    var eError:String?

    

    let sup = SignUpVC() // here what caused the error

    

    //MARK: - SignUp

    func signUp(email:String, fullname:String, username:String, password:String){

         

        Auth.auth().createUser(withEmail: email, password: password) { (authResult, error) in

            if let error = error {

                let errorText = error.localizedDescription

                if errorText == "The email address is badly formatted."{

                    DispatchQueue.main.async {

                        self.errorEmail()

                        

                    }

                } else if errorText == "The password must be 6 characters long or more."{

                    DispatchQueue.main.async {

                        self.errorPassword()

                    }

                    

                }

                print(errorText)

            }else {

                //self.clearTextFieldColor()

                let userID = Auth.auth().currentUser?.uid

                var add = self.db.collection("userinfo").document(userID!).setData(["fullname" : fullname,

                    "username": username])

            }

        }

    }

ViewController
import UIKit

import Firebase



class SignUpVC: UIViewController{



    @IBOutlet weak var emailTextField: UITextField!

    @IBOutlet weak var passwordTextField: UITextField!

    @IBOutlet weak var fullNameTextField: UITextField!

    @IBOutlet weak var userNameTextField: UITextField!

    @IBOutlet weak var facebookBtn: UIButton!

    @IBOutlet weak var signupBtn: UIButton!

    @IBOutlet weak var errorText: UILabel!

    

    let db = Firestore.firestore()

    var signUp = SignUp()

    var err:String = ""

    

    override func viewDidLoad() {

        super.viewDidLoad()

        

        facebookBtn.layer.cornerRadius = facebookBtn.frame.height/5

        signupBtn.layer.cornerRadius = signupBtn.frame.height/5

        signUp.emailTextFieldCopy = emailTextField

        signUp.passwordTextFieldCopy = passwordTextField

        signUp.fullnameTextFieldCopy = fullNameTextField

        signUp.usernameCopy = userNameTextField

        

    }

    

    override func viewWillAppear(_ animated: Bool) {

        errorText.text = err

    }