Solution 1:

The following lines should be updated in app -> main -> res -> values -> Styles.xml

 <!-- Application theme. -->
<style name="AppTheme" parent="AppBaseTheme">
    <!-- All customizations that are NOT specific to a particular API-level can go here. -->
    <item name="android:actionOverflowButtonStyle">@style/MyActionButtonOverflow</item>
</style>

<!-- Style to replace actionbar overflow icon. set item 'android:actionOverflowButtonStyle' in AppTheme -->
<style name="MyActionButtonOverflow" parent="android:style/Widget.Holo.Light.ActionButton.Overflow">
    <item name="android:src">@drawable/ic_launcher</item>
    <item name="android:background">?android:attr/actionBarItemBackground</item>
    <item name="android:contentDescription">"Lala"</item>
</style>

This is how it can be done. If you want to change the overflow icon in action bar

Solution 2:

I got a simpler solution which worked perfectly for me :

Drawable drawable = ContextCompat.getDrawable(getApplicationContext(),R.drawable.change_pass);
        toolbar.setOverflowIcon(drawable);

Solution 3:

//just edit menu.xml file    
//add icon for item which will change default setting icon
//add sub menus


 ///menu.xml file


    <item
            android:id="@+id/action_settings"
            android:orderInCategory="100"
            android:title="@string/action_settings"
            android:icon="@drawable/your_icon"
            app:showAsAction="always" >

            <menu>

                <item android:id="@+id/action_menu1"
                    android:icon="@android:drawable/ic_menu_preferences"
                    android:title="menu 1" />

                <item android:id="@+id/action_menu2"
                    android:icon="@android:drawable/ic_menu_help"
                    android:title="menu 2" />

            </menu>
        </item>