This question popped up again when we were teaching Planner to a client. Its not the first time we have been asked. You might have noticed this when working in Excel online or other 365 Apps like SharePoint, OneDrive, Power Automate or Loop. The dates all default to the American format of MM/DD/YY.
Here's how to change your dates to NZ format!
This only changes your date format. To change date format for all users you will need your administrator to change this in the Admin portal.
Here are some helpful links:
Change regional settings for a site - Microsoft Support
Set language and regional settings for Microsoft 365 - Microsoft 365 | Microsoft Learn
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