There is no actual button, there should be one to the right of Google Play Store that says ‘Turn On’.
If that button was on that Settings page, I’d be good to go and presumably could install your app and other Android apps, but it’s not there.
As you suggested - and that’s smart in order to cover all the bases - I did click on what is there, i.e., the Google Play Store text (the arrow to the right of that also goes to the same place), it takes me to the settings page shown in the image below. I then clicked on the Manage Android Preferences option and since I can’t install Android apps, there’s nothing to manage.
