A backup can only be deleted after it has been archived.
A backup is automatically archived when BackHub can no longer access the original repository at GitHub. This occurs when (1) access is revoked for the installation, (2) access is revoked for this specific repository, or (3) if the original repository has been deleted on GitHub.
Archived backups are listed in a separate section at the bottom of the page and indicated by a dashed outline.
When you delete a backup it is permanently removed and can no longer be restored. The Delete button is in the footer section of the backup panel.