Nick...
The letter your dealer has sent you refers to this TSB Number: 23-050-06 REV. A Subject

ower Door Lock(s) Inoperative. Once a vehicle leaves the dealership and a customer reports a problem, like in this case with the power locks, that is known a repair procedure is documented and distributed to the dealers as a Technical Service Bulletin.
But before a vehicle is sold, dealers sometimes receive what are called Rapid Response Transmittals from Chrysler to inspect vehicles if there is a possible component malfunction, again in your case the power locks. The repair procedure is done before the vehicle is delivered to a customer. #06-058 Power door locks is the document number that dealer received as a Rapid Response Transmittal on your Nitro.
Your Nitro may or may not require this repair. If your locks are working normally, you can inform your dealer there isn't a problem. Hope this helps.