basically I have an app that consist of events, there are events registered on different times. I have local notification through which user get to know that his event is there before 15 minutes according to the requirements. It is working when the app is in use but when the app is killed notification is not appearing i want local notification to be appear when the app is killed ! Ionic 7 Capacitor 5 What to do 
You need to provide more information. Are you having issues on Android or iOS? How are you creating your local notifications?
On Android, you might need to use USE_EXACT_ALARM - see (Android) Ionic local notifications are not delivered on time - #2 by twestrick
I am creating my notification as per the capacitor document it is getting called on the constructor for both iOS and Android. In android it is working some how “don’t know how” but in iOS when we start the app that time we are getting notified.
Please share your code in how you are creating the local notification.