How to start the function when the application is closed

I have an echt function that accepts nothing and returns nothing. Inside the function there is a check for dates if the current day matches the notification. When the application is running, everything works fine, and if the application is closed and the next day comes, the function does not work, you need to restart the application so that the function starts how to solve the problem so that even if the application was closed all the time, the function worked