The answer to this question is very simple. No, you can not trademark the app itself. You can not trademark what the app does. You can not trademark the idea behind the app. You can not trademark the technology that makes your app possible. None of that is something you can trademark. What you can trademark is the name of the app. You can trademark the logo for the app if you have one. And you can trademark taglines, the slogans that those catchphrases that you use to promote your app.
Those are the things that you can trademark but again you can not trademark the substance behind the app.