@Manju_Nath you can get to the Android Home by using the .press_keycode(3) method. I have an example on python that goes to the android home screen, and then opens the Chrome app. You might be doing the same but checking for the Whatsapp button.
Once you manage to open the Whatsapp app, I will recommend you to get the elements displayed by using .page_source, and go from there step by step of what you are planning to do.
You can reuse some of this code; https://github.com/Urucas/AppiumTests/blob/master/open-browser/test.py
