1. If you are performing a fresh installation of Windows 10, you will be prompted to enter your code during installation
2. After you complete the installation, follow the instructions in Step 3
3. If you want to enter/change your product key within Windows 10. Go to settings
4. Select Change Product key
5. Enter new Product key & click next
6.To activate Windows 10 by Offline: Press the Win+R keys to open Run, then type: SLUI 4, then click on OK. (Note that there is a space between SLUI and 4.)O
7. Select your country or region, then click Next.
8. Then you will get the Installation ID screen, Note down the Installation ID. This required to get the Confirmation ID to activate.
9. In the Windows 10 Creators Update and later versions, contacting support is now available in a new app called Get Help. Open Get help. Other OS version can open it from this web link. https://support.microsoft.com/contactus
10. Type Activation in the chat window then press Enter.
11. Click Windows 10 or Appropriate windows OS to activate.
12. Select Activation After Reinstallation Windows 10
13. Click No
14. Click A different PC
15. Type Error code as 0xC004C008
16. Click No
17. Click Yes
18. Enter Installation ID
19. Now you will get Confirmation ID, note down it and fill it on your activation screen. Then click activate windows
20. Verify windows is activated