I hope this works. Apple: "Please use the Beta Access Utility to update your Developer Transition Kit to the latest macOS 11 Big Sur beta. Download the image by visiting the Universal App Quick Start Program site and selecting Beta Access Utility. Once you’ve installed the Beta Access Utility, it will locate the latest update available.
If the update is stuck at the “Restart” dialogue stage, please hover your cursor over the notification window and wait a moment for the option to appear. If you encounter any issues during this process, please submit a new feedback report through Feedback Assistant with a sysdiagnose and description of the issue.
Thank you!"