To remove Canopy from Chromebook you will have to approve a request from the device:

1. On the Chromebook, open Canopy app.
2. Open the side menu and select Remove Canopy.
3. Click on Send request.
4. Exit the app.
5. Respond to the request on the Parent app or Dashboard
6. Open the app on the Chromebook again and you will see the option to Remove Canopy on the main page. 
7. Approve the removal both on the Android system and the web.