If your system has missing database tabled, there are a few options to resolve them.
1. If it is not needed, you can delete the Class too (through the Kentico Admin)
2. If you do need it, and it was renamed, you can rename the table back to what it was (or change the Class info in the database). Change the class's table name is a little tricky but very doable if you are comfortable with SQL.
3. If you need it, and it was deleted, you will have to restore backups and bring the table back over to your database
4. if you need it, but there was not any live data in it, you have the option to delete it in the Kentico Admin, and rebuild it from scratch.