The only way I know is thru your dealer. They have/had an offer recently for about $126 (I think) if you got it done as part of a service. Or more expensive if stand alone.
I updated maps on my E3 HSV a few years ago. What a waste of time. The maps were still way out of date. I don't use either of the in car Sat Navs. I use one on my phone always - Waze. Hardly uses any data and im in the car at least 2.5 hours a day with it on. Tells you of police speed traps and other road condition issues and the live traffic ETA estimates are always with in 2-3 mins.
What database do you currently have?
You could contact https://www.envyouscustoms.com/ or the likes, I have gotten a map update off him before but can’t see it on his website at the moment.
As voodoo says though it’s probably not worth it as it will already be out of date. Something like google maps is usually pretty good with live traffic and pretty accurate with ETA’s etc, I have tried waze before but personally found it to be absolutely crap and not nearly as good as google maps (even though google owns waze) but each to their own.
Sounds like a pretty BS excuse to me.
Check out the below, can be copied from GM online you just need to have the right cable and a subscription which is only like $40 for 2 years.
So I paid for a 2 day subscription for GM online service programming and whilst updating the various modules, I found an option to copy Navi data to SD card
The instructions state you will need a separate SD card which is used for configuring and updating the existing MAP SD card.
I'm pretty sure it worked because I had a MY12 SD card but now have the latest maps