How to Activate Windows 10 by Phone
To activate Microsoft Windows by Phone method, follow the guide below:
1 To enter/change your product key within Windows 10, follow the screenshot below.
(Start > Settings > Update & Security > Activation > Change product key)
2 - You will be prompted to enter product key. Enter your product key purchased. Then, click "Next".
3 - After entering the product key, you will receive the following error code 0x803F7001.
4 - Press Windows logo key + R key to open Run, then type: SLUI 4, then click OK. (Note that there is a gap between SLUI and 4).
5 - Select your country or region, then click Next.