Unresolvered reference: when I call the method of an instance from another activity

Question

I would like to call the method of an instance of AuthActivity from MainActivity. However, I get an error. AuthActivity contains a variable that lets you know if the user has already authenticated from this activity!

Unresolvered reference: checkIfUserAlreadyLogged()

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        FirebaseApp.initializeApp(applicationContext)
        setContentView(R.layout.activity_main)

      
        if (AuthActivity.checkIfUserAlreadyLogged()) {
            return this.displayAuthWithFragment(AuthActivity.HOME_FRAGMENT)
        }

    }
 }

Here is my AuthActivity class:

package com.ksainthi.inance


import androidx.appcompat.app.AppCompatActivity
import androidx.activity.result.contract.ActivityResultContracts
import androidx.fragment.app.Fragment
import com.google.firebase.auth.FirebaseAuth

class AuthActivity : AppCompatActivity() {

    private val firebaseAuth: FirebaseAuth by lazy {
        FirebaseAuth.getInstance()
    }


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_auth)

    }


    fun checkIfUserAlreadyLogged(): Boolean {
        if (this.firebaseAuth.currentUser != null) {
            return true
        }
        return false
    }
 }