Iphone 5s, on IOS Version 12

My iPhone 5s has been running on Version 12, i never upgraded to any newer Version

because memory is only 16 GB. Yesterday there was an upgrade on one of the mobile Applications which I use. After doing the upgrade the Application stopped working, it opens for a few seconds and goes off.

I tried deleting the application and reinstalling as advised by the Application support staff but it still doesn't work.

The same application has been working on my iPhone since many years. Need help please.

Thank you