You may need to delete all the data in your Deskpro installation and start again from scratch (for example, to get rid of test data and start using the helpdesk for real).
Note that this procedure removes everything from the helpdesk: not just tickets, but agent accounts, user records, custom triggers, admin settings - everything.
Here's what to do:
1. Make sure to copy down your license code from the Billing interface (dollar icon at lower left).
2. Delete the Deskpro MySQL database (as specified in config.php).
Alternatively, you can just enter a different database name in config.php:
If you do this, Deskpro will make a new empty database with the name you choose, but the old test database will still be in MySQL.
3. Delete the is_installed.dat file in the Deskpro /data directory (where you unzipped the Deskpro files during installation). If this file is present, Deskpro will treat the missing database from step 1 as an error; removing it tells Deskpro to initiate the install process instead.
4. When you go to the web interface, the Deskpro install wizard will run. A new empty database will be created. Since you haven't changed anything about your webserver/cron or Scheduled Tasks configuration, you should be able to click through each screen of the install.
5. Enter the license code you noted down in step 1.