My download of macOS Sierra (Developer Preview, see press release) began downloading, appearing in the Launchpad app. But then got interrupted. It failed to restart, so I deleted the icon in Launchpad by holding down Option key and clicking the "X" icon that appears.
Now when I try the download again, the link on the Developer page takes me to the App Store app. There I get page with a
Redeem button and an error message saying “This code has already been redeemed.”.
How can I restart the download?