Hi,
From the following blog, it offers the following guidance temporary workaround until such an update can be properly created, tested, distributed, and installed. Thanks for your understanding.
Interim Guidance for Tonga
Until an update is made available, we recommend our customers who have selected “(UTC +13:00) Nuku'alofa” to disable the "Adjust for daylight savings time automatically" option in the Date & Time Settings page. Doing so will correctly
reflect the time in Tonga.
Time Zone Updates for Fiji, Cyprus, Sudan, Tonga, Namibia and Turks & Caicos
https://blogs.technet.microsoft.com/dst2007/2017/10/25/time-zone-updates-for-fiji-cyprus-sudan-tonga-namibia-and-turks-caicos/
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