How to design an app that continues to save data from where it left off every time it is restarted?

Actually l asked this questions a few days ago but l could'nt get an answer, so here am l again.

I have a calculator-like app. To see the data in the app, it uses a UITable with a variable, defined as unique property, that increases each time a button is pressed. When the application restarts, UITable and associated variable are reset. Is there a way to keep them from being reset and force them to carry over from their previous work?

Additionally, the app stores data in an excel file. Every time I restart the program, it overwrites on the excel. I must ensure that I can write the data after the preceding data without losing any of it.