There is a registry branch called "Inventory" under the VST branch. It contains all the items that were scanned. You can delete the branch (do backups!) or just delete items in it.
I don't recommend doing this if you're not a serious computer hacker type ;)
But it's a lot simpler than the plugin manager.
However, IF there are other issues (left over DLLs as example, or bad installs, or corrupt registry entries) you'll just be adding misery as opposed to cleaning up.
Doing a complete VST Reset is often the better approach after you clea up any subsidiary issues.