Hey there, robmerobu!
Thanks so much for using Apple Support Communities.
After the end of that waiting period, you will be able to associate your device with your current Apple ID by setting up Apple Music on that particular device. As soon as you subscribe to a service or purchase content on the iTunes or App Store, your device will automatically be associated with your Apple ID so long as you haven't reached the device limit.
This article has some more information: View and remove your devices that are associated with Apple ID purchases - Apple Support
While you're waiting for that 12 day period to end, you may want to remove any other devices you're no longer using so that you're set for the future if you want to set any other devices up down the road. The article we shared previously will have the steps to do that.
We hope that this information is helpful.
Have a great day!