AIR was removed from the Google Play store in September. Your only solution is to do an app update, to include the embedded AIR runtime. The overhead of the runtime is under 9 MB, and with most recent phones that wouldn't be much of a problem.
Another thing for you to know about is that Google Play now require a minimum Android SDK level of 26, I think. To get that you would want to publish using a recent version of AIR, might as well use the current release version.
A consequence of supporting that SDK is that you may need to change how you do permissions. From Android 6 the way permissions are done changed, to be more like iOS. Adobe solved the support for that in AIR 24, and the release notes for AIR 24 tell you how to write your code to support Android 6: