title: Android app signing: for an existing app with "OPT OUT", can I change it to [App signing by Google Play]
body: <ol>
  <li>As the title, we released an app but had selected the "OPT OUT" as the attached screenshot. Can we change it to [App signing by Google Play] as like clicking the [Continue] button?
  Because this app was released for a year, and got some users, we do not want to create another app to replace it and restart again.</li>
  </ol>
  
  <p><a href="https://i.stack.imgur.com/DeVja.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DeVja.png" alt="The screenshot when first app release"></a></p>
  
  <ol start="2">
  <li>It looks like we should go to [App signing] of the existing app to do the option [You've exported your app signing key](as the screenshot below).
  But when uploading the key store file used in Android Studio [Generate Signed APK], it appears error. In fact, we do not exactly understand the logic of key files. Any idea or experience is welcome.
  <a href="https://i.stack.imgur.com/yhwbv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yhwbv.png" alt="enter image description here"></a></li>
  </ol>