Need Help，I want quit preview

Sorry to see you leave the preview program. You should be able to leave the program using the option in the Dashboard Preview App. Be aware that you will remain in the current preview until it is fully released to the public.

If you are having issues using the option to leave the program from the app then you can post in the preview forums.

forums.xbox.com/.../default.aspx

I want out if update preview. Need help.

Hey, guys! If you're in the preview program, you'll want to post this up in the
Update Preview Forums. They'll be better suited to help you out or flag this as something that needs to be fixed.

The xbox support said I'm in the preview program but I never revived the message on my console.

Hi folks,

being invited to the preview program does not guarantee selection. And bear in mind that they do invites in batches/waves due to volume of people trying to join.

How will you know if you are selected?

You'll get a service message from the team on your Xbox One. The message will include a link to download the Xbox Preview Dashboard app. You'll need to use the app to register your console for Preview updates.

There is more info available on the official FAQ
here

My advise is to be patient - if you are not selected during this wave you can get re-invited but I suggest you wait at least a month between invites.