Please post a ticket to our account service team, who will be able to get that sorted for you. Click on your license in the client area, select to create a support request, and you will see a contact us link in the description below the 2 options for support
Please keep in mind that this is not suggested (or supported) as there are many relational tables within the database and if you don't get every instance, it can completely brick your installation. The worse part of this, is you may not know till later down the line.
This is why we recommend doing everything via the software itself. You can use the "Move/Delete content" option in ACP -> Community -> Forums to delete content or the whole forum.
