Calm is a meditation app. They discovered that a crucial key to retention wasn't part of the core app itself but in getting new users to set a daily reminder. Here's a guide jumping off that discovery on triggering product usage for the long-term.

I want to display ads on mobiles who are in Geo-fence and don't have my app downloaded on their mobile. How I can do so?

I am a big fan of AARRR. But it has one major issue: it focuses on Acquisition instead of Retention. And that will destroy your mobile startup.