There's no automatic function to restore your database. Please follow these instructions:
If you are using a Microsoft Access database or a SQLite database, Xpert-Timer creates automatic backups in the standard setup. If you are using a MySQL or MS-SQL database, you have to create your backups on the server manually or use XTAdmin in order to create a backup.
How to find the backup file:
The database backups are saved in the format: xt_20120630_10-47.mdb bzw. xt_20120630_10-47.sqlite (depending on what database you use).
20120630 stands for: June 30th 2012. 10-47 stands for 10:47 am.
In case you don't remember where your database is stored, search for xt_* in your file explorer.
Steps to restore your backup:
1.) Once you've localized the newest backup, create a copy of the file.
2.) Rename the copied file to xt.sqlite for SQLite or xt.mdb for access.
3.) Navigate to your original database folder (search for xt.mdb or xt.sqlite in your file explorer) and replace the file with the just copied and renamed one.
4.) Start Xpert-Timer. If the file still doesn't work, try it with a file that's one day older.