To send feedback to Google, you can refer to some of the following:
1. On your device click on Android N Quick Settings or open Settings => About => Send feedback about this device.
2. Upload your comments on the Android Beta Program Google+ community.
3. Report bugs on Android Open Source Project Issue Tracker (for developers only).
For some reason you want to unsubscribe from the Android Beta Program, such as Android N with too many errors . Very simply, you just need to follow the steps below:
1. Visit Abdroid Beta Site on your device or on the computer.
2. Log in to your Gmail account, then scroll down to see if your device is eligible.
3. Click Unenroll Device and accept to reset the whole device (factory reset) when notified.
Note : All data on the device will not be backed up and will be erased after you exit the testing process.
Within 24 hours, your device will receive a notification of an appropriate Android update to download and install, which may be Android Marshmallow version.
Good luck!