I have a question!

This is not a regular post. I have a question if you people can guide me.
I am Electrical Engineer and interested in android programming. I like to modify app values through source code modification (not for harmful purposes obviously) and I literally do it correctly. I can change the UI of app and many more. But the thing is that data is not modified in existing SQL database. neither on server neither on android. Any tricks to modify data through within the app?
Thanks in advance developers!