The esd file is in the $Windows.~BT folder which is hidden. And to be precise, the file is in the Sources directory underneath the $Windows.~BT directory.
oops, almost forgot, you should have gone into Windows Update and downloaded this build before the ESD file will appear.
The Edge browser should be minimized. Then you will get a toast notification and that message in Action Center. If Edge is active, you will not be notified.