If you are getting both a new Windows Phone and a new phone number, use our Change Number feature before you transfer your chat history to the new phone.
To transfer your chat history from your old Windows Phone to the new one, please check the following requirements:
If all requirements are met, you can transfer your chat history by simply moving your external SD card from your old device to the new one. Otherwise, you will not be able to transfer the chat history at this time.
After inserting the SD card to your new phone, install WhatsApp from the Store and tap restore when asked if you want to restore your chat history.
You can also export your chat history by emailing the chat history to keep a record of your chats. Please see this article to learn how to email your chat history.
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Cheers,
WhatsApp Support Team