Yeah that page which was linked to isn't really part of the website: it's a separate site entirely, which is a frontend to the data-collection service.
People aren't really supposed to link to it directly as a means of introducing new people to Syncthing...
One of the common complaints about Syncthing is the lack of native UI (you use your web browser), and the difficulty in setting it up for non-technical users (copying an executable into a directory, running it directly, setting it to automatically start on login aren't something you'd ask your parents / grandparents to do).
There are a number of projects which make life easier for Windows users (tray icon, autostart, make it look and feel and bit more like a Windows application, bundle filesystem notifications, etc). Two of the big ones are SyncTrayzor (https://github.com/canton7/SyncTrayzor) and Syncthing-GTK (https://github.com/syncthing/syncthing-gtk).
1) There's no way to revoke access, and 2) Once the secret is out, it's out: you have to scrap it and start again from scratch.