If a device(s) is registered to a user and needs to be registered to another user, delete the user from the device.
Individual User and Device
To delete an individual user from their registered device, log in to the web filter and navigate to Reports > Network Access > Mobile Devices. Find the device in the list of Mobile Devices, and click Delete (in the Action column).
All Users and Devices
To delete a all users from their registered devices, log in to the Web Filter and navigate to Web Filter > Mobile Devices and click Delete all mobile devices.