How can you re-engage users who have abandoned your app after their first use?
By offering store credit for users who click your ads
By engaging users who visit your desktop website
Remarket to app users with a compelling message across search, display, and video.
Offer deeper discounts to entice visitors.
There must be some subscribers who logged in to your app using the mobile number and email IDs. You may have stored those. Reach out to them with promotional content through those methods.
If they haven’t uninstalled the app, you could release frequent updates, and add more features. Rich features and graphics along with usability increase app use.
You could also send them notifications, announcing new feature or advertising the existing ones.
These are some ways.
Read more here: https://support.google.com/partners/answer/6167164