Hello,
Not really sure if I understand you here, do you mean you want to delete all the existing tables that was created by EasyDiscuss and start a fresh installation?
Currently when you uninstall EasyDiscuss, it doesn't remove the data from the site. This is to prevent admins who accidentally uninstall EasyDiscuss from the site.
If you want to start a fresh install:
1. Uninstall EasyDiscuss
2. Delete the tables with the prefixes of #__discuss_*
3. Install EasyDiscuss again