I want to build this to my application but I dont know how. Could anyone help me with this?
(Tip: You can also ask users to upgrade to the latest version of your app using the Google Play Developer Publishing API. This solution allows you to target the entire range of application versions as well as individual application versions.)
At first, I thought that I just had to go through the steps, but in principle, something must be included in the application.
write a clone version of Taifun's InAppUpdate extension and use your extension in your app? This will require a lot of work.
if your app uses CloudDB or FirebaseDB, you might be able to post a message in your app that users 'see' when they access the app. The message would provide instructions on how they could download the app from your Dropbox (yes, you would have to upload a copy of the upgrade to the app there)
if your app requests email addresses in order to use it, you can email all the users to log in to it. Email to tell them there is a new version available on your Dropbox.