Android : Update Available message appears automatically - android

May I ask you a question?

I built an android application but it's not on google play store. I would like to add an update alert message there so i try WVersionManager - https://github.com/winsontan520/Android-WVersionManager. It clearly run in test but nothing happened after clicking "Update Now" button.

The main problem is where can i add my application apk link - I uploaded update_content_json_format.txt and it worked well. That text file is only for the update information -

{"version_code":2,"content":"Version 2.0
<p>New features:</p>
<li>Added feature A</li>
<li>Added feature B</li>
<li>Added feature C</li>
<li>Added feature D</li>
<li>Added feature E</li>
<li>Added feature F</li>
<li>Added feature G</li>"}

please point me where can i add my update application apk link which is not from playstore.

-- or --

According to the idea, I would like to know how to show update available dialog box automatically whenever I open the application.

Thank you very much!

With Regards,