The ZAGG Protect subscription is non-transferrable. Since the plan is assigned to a device's specific IMEI number, if you upgrade to a new phone you will need to cancel your current ZAGG Protect plan and purchase a new plan. You will then need to run the diagnostic on the new phone and wait the 30-day grace period for coverage to begin.
If you can't find the email that contains the diagnostic link simply visit ZAGG.safeware.com, click on "Register Your Device" to bring up a QR Code. Scan that QR code with your phone's camera and you're on your way.