Q: How do I delete goodnotes backup on iCloud?

The following may help: Manage your iCloud storage - Apple Support

It is not clear what it is that you tried.

If you have a computer you should be able to go to https://www.icloud.com/ and log in. Then click the iCloud Drive icon at that site, select the file in question and then click the trashcan icon near the top of the window.

From your phone you should be able to do the following (from the link I provided previously):

iOS

You can use these steps to manage your files from your iPhone, iPad, or iPod touch:

1. Tap Settings > iCloud.
   • If you're using iOS 8 or later, tap Storage > Manage Storage > iCloud Drive.
   • If you're using an earlier version of iOS, tap Storage & Backup, then tap Manage Storage.
2. Tap the name of the app that's using iCloud Drive.
3. The individual files in that app will appear. You can either swipe left or click the Edit button to remove files.

I have the same issue. Every backup to iCloud decreases free space in the iCloud. And I even can't remove the latest visible backup. So all devices stops work because I don't have enough free space in the iCloud and I can't clean up it. WHO CAN HELP???

http://remove iCloud