On what platform, please?
On Android, any files you store locally on your device should be utterly unaffected by deleting/reinstalling the app.
On iOS, when you save files locally, they go into the apps 'sandbox'. This means that when you delete the app, you delete all the files that were created with it too.
I'm sorry, but that's just how Apple decided it should work. I'm afraid your files are gone for good