Safety first: Before modifying application files, you should always consider creating a backup to which you can revert if something goes wrong. You might need the pro version in order to do that.
I did not create a backup – and now?
If an app is broken and you do not have a backup available, the easiest way to fix this is to reinstall the app. This will result, however, in a loss of all your data. So if it is a game which you tried to hack, you would have to start all over. This is not always the most satisfying solution, but it might be necessary. Except, of course, you remember the changes you made and revert them manually!
Please note that we do not assume any liability if you mess up your device or the functionality of other apps.