Hi, I'm Nathan.Sorry to hear that you're having trouble with this but I'll do my best to help you.
Unfortunately, Douglas, this is not possible to change over.
The model you purchased is purpose built for decoding only the broadcast format used in AU. It is not compatible with the NZ over the air signals. This restriction is hardware coded, and not something that can be changed via a code or software setting.
The item you would need is the DMR-PWT550GZ, which is the NZ specific model capable of working in your location.
Hopefully the store where you purchased the original one will understand the location restriction and allow you to return it.
Best regards, ***** ***** for the news,
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