After you disconnect a cloud storage from your NewscasterVocalizer Settings, if you want to completely remove the App from that cloud storage you need to remove app access from that cloud storage account. This may be required in case you need to add the same cloud storage but with a different account.
You need to login to the respective cloud storage account first.
Click on your Profile Photo on top left, Go to Settings, Go To Connected Apps, Scroll down and remove NewscasterVocalizer under Apps with access to your Dropbox.
You may remove the granted access for your bucket from access control list. Please check AWS documentation for more details.
Or, simply download the files and delete that bucket.
Click on your Profile Photo on top right, click on Google Account, go to Security, scroll down and remove NewscasterVocalizer under Third-party apps with account access.
To remove, click Third-party apps with account access, then click NewscasterVocalizer.
And, click REMOVE ACCESS.