New Outlook - date format problem with imported CSV contacts

Because the format of contacts in new Outlook has changed, New Outlook requires contacts to be exported from old Outlook, and imported into new Outlook. I have my locale set to Australia in both new Outlook and old Outlook. I exported my contacts from old Outlook to a CSV file. When I open the fil e in Notepad, I can see that birth dates are in d/m/yyyy format (eg, 20/8/1960). When I import the file into new Outlook, dates with a day that's 12 or less are being interpreted as US format (m/d/yyyy), so that a date of 5/8/2023 (5 August) is being imported as 8 May. And dates with a day of 13 or above are being discarded because the import process thinks the day is actually the month. Any advice on getting around this would be appreciated.