Restoring a backup on iOS
Studies for iOS makes internal backups, so if something really goes wrong, you may be able to get your data back. (Warning: It is always better to keep your own system wide backup with Time Machine on macOS, or iCloud on iOS.)
To see if there is a backup, go to the menu that lists iCloud Sync. On iPhone, you tap the top-left button to open the menu. On iPad, it is in one of the menus top-right.
Now tap on the "iCloud Sync" row with three finger tips together. It can take a few tries to get this right, but if you do, you should see a list of backups, and you can choose to restore.
Please only use this in cases of emergency, where your data is completely corrupted. Note also, the backups will be deleted if you delete the app, so reinstalling will remove these backups. In that case, you would need to rely on a backup on your Mac, or data in iCloud, or the iCloud backup of your whole device.
Studies for macOS and iOS
Mental Case for Mac OS X
Mental Case for iOS