In Order to display action bar back button in Kotlin
there are 2 way to implement it
1. using the default Action Bar provided by Android
    - Your activity must use a theme that has Action Bar
    - eg: Theme.AppCompat.Light.DarkActionBar
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    val actionBar = supportActionBar
    actionBar!!.title = "your title"
    actionBar.setDisplayHomeAsUpEnabled(true)
    //actionBar.setDisplayHomeAsUpEnabled(true)
}
override fun onSupportNavigateUp(): Boolean {
    onBackPressed()
    return true
}
2. Design your own Action Bar
   - disable default Action Bar
   - eg: Theme.AppCompat.Light.NoActionBar
   - add layout to your activity.xml
    <androidx.appcompat.widget.Toolbar
     android:id="@+id/main_toolbar"
     android:layout_width="match_parent"
     app:layout_constraintEnd_toEndOf="parent"
     app:layout_constraintStart_toStartOf="parent"
     app:layout_constraintTop_toTopOf="parent">
     <androidx.constraintlayout.widget.ConstraintLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         tools:layout_editor_absoluteX="16dp">
         <TextView
             android:id="@+id/main_toolbar_title"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="Your Title"
             android:textSize="25sp"
             app:layout_constraintBottom_toBottomOf="parent"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintHorizontal_bias="0.5"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toTopOf="parent" />
     </androidx.constraintlayout.widget.ConstraintLayout>
 </androidx.appcompat.widget.Toolbar>
override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     setSupportActionBar(findViewById(R.id.main_toolbar))
 }
<?xml version="1.0" encoding="utf-8"?>
<menu
 xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res-auto" >
 <item
     android:id="@+id/main_action_toolbar"
     android:icon="@drawable/ic_main_toolbar_item"
     android:title="find"
     android:layout_width="80dp"
     android:layout_height="35dp"
     app:actionLayout="@layout/toolbar_item"
     app:showAsAction="always"/>
</menu>
override fun onCreateOptionsMenu(menu: Menu?): Boolean {
     menuInflater.inflate(R.menu.main_toolbar_item, menu)
     leftToolbarItems = menu!!.findItem(R.id.main_action_toolbar)
     val actionView = leftToolbarItems.actionView
     val badgeTextView = actionView.findViewById<TextView>(R.id.main_action_toolbar_badge)
     badgeTextView.visibility = View.GONE
     actionView.setOnClickListener {
         println("click on tool bar")
     }
     return super.onCreateOptionsMenu(menu)
 }