I have a Phantom 3 4K, which has been sitting unused in a container in my room for three years. Just now I am learning of the new FAA regulations which stipulate "Remote ID." How do you get Remote ID for this (old) drone? I read that DJI is releasing firmwire updates for drones that were not originally released with built-in Remote ID.

There's no need for remote ID until September 2023.    At the moment only a few models have had remote id updates which is required for them to continue to be sold.  

Not sure if the old Phantom 3 will get remote ID via firmware update.  You will probably have to add a remote ID module.  

DAFlys Posted at 3-6 00:36
There's no need for remote ID until September 2023.    At the moment only a few models have had remote id updates which is required for them to continue to be sold.

So, can I just reregister the drone and fly it now while waiting for the firmware? Is that legally safe?

Person123321 Posted at 3-8 13:03
So, can I just reregister the drone and fly it now while waiting for the firmware? Is that legally safe?

Quite legal to do that.