How can I randomly reward points for app usage

I am working on an android app where user get points for using the app which can be used to unlock in-app features.

I have a function called rewardPoints() which generates random integer and I want it to get called randomly while the user is using the app. The points then gets added up in database.

fun rewardPoints() { var points = Random().nextInt((5-1) + 1) }

How do I call the function rewardPoints() randomly while the user is using/interacting with the app?