Where do I find my DJI Care reference numbers to register it against my drone?

Hi, there. Thank you for reaching out.
If you purchased DJI Care Refresh from DJI Store, it will be bound to your product automatically and come into effect within 24 hours.
Only when you have a DJI Care Refresh physical card, which is normally purchased from the retail store you'll need to enter the activation code.
You may confirm if the DJI Care Refresh has been activated by checking the balance at DJI official website > Support > DJI Care Refresh > CHECK YOUR DJI CARE REFRESH.
Hope this help.