This link to YouTube shows how to replace the modem component of the MCU once it’s taken out of the car.
It shows the location of the SIM within the MCU as well and promises a link to another video showing how to remove the MCU itself. There are a number of YT videos showing how to remove the MCU like this one in any case.
If the car is already on its way I would go to Auckland service and ask nicely for them to put in a NZ SIM for you, but be ready for a flat no.
A competent mechanic should be able to do this for you if all else fails.