If you no longer wish to use Alexa on a Nucleus device, you can simply log out from Settings > Amazon Alexa. If you don't want that device to appear in the Alexa mobile app any longer, you can remove it from your account on the Amazon website.
- Go to Manage Your Content and Devices on Amazon.
- You may be prompted for your Amazon login here. If so, sign in.
- Click the Your Devices tab on the page that loads.
- You'll see your Nucleus devices listed here among all your other Amazon connected devices. Click on the Nucleus you wish to remove.
- Click Deregister.
You should no longer see that Nucleus device listed in the Alexa mobile app. If you'd like to add it again, just sign back into Alexa, also in Settings > Amazon Alexa.