Hi Victoria, sorry for the delay in getting back to you. If you are using the latest version of younity you can now unregister your own devices from any other device.
On your new iphone, go to Settings scroll down to Devices and find the old phone. Click on the "i" icon next to it and then scroll to the bottom of the Device Details page.
You will see an "Unregister <devicename> button. Click on that button and your device will be unregistered.
If you are not running the latest version of younity and don't have this function available, please let us know which device (the actual device name) that you want us to unregister. I don't want to unregister the wrong one by mistake.
i have the same issue... could you pls unregister my old phone?