Yealink has changed how you go about removing a device that is already registered to RPS. Before you could create a ticket with their support. Now you need an RPS account or a Yealink Cloud Management Service account. RPS Can be setup here: https://www.yealink.com/en/onepage/yealink-free-remote-provisioning-service
Once Logged in to RPS portal. Navigate to "Device"
From there in the top right is Release Occupied Device.
Select Release Occupied Device and enter MAC and SN. Now the device has been removed from RPS and can now be added to kazoos for registration.