Using the Activation troubleshooter after a significant hardware change
After you add your Microsoft account and link it to your digital license, you can use the Activation troubleshooter to help reactivate Windows after a significant hardware change.
If you didn't add your Microsoft account and link it to the digital license on your device, you won't be able to use the Activation troubleshooter to reactivate Windows after a hardware change.
Select the Start button, select Settings > Update & security > Activation , and then select Troubleshoot. You must be signed in as an administrator.
The troubleshooter will show a message that Windows can’t be activated on your device. Select I changed hardware on this device recently, and then select Next.
Enter your Microsoft account and password, and then select Sign in. You’ll also need to enter the password for your local account if the Microsoft account you entered isn’t a connected account.
From the list of devices that are linked to your Microsoft account, select the device that you’re currently using, select the check box next to This is the device I’m using right now, and then select Activate.
If you don’t see the device you’re using in the list of results, make sure that you’re signed in using the same Microsoft account you linked to the Windows 10 digital license on your device.
If you’re signed in using the correct Microsoft account, here are some additional reasons why you can’t reactivate Windows:
The edition of Windows on your device doesn’t match the edition of Windows you linked to your digital license.
The type of device you’re activating doesn’t match the type of device you linked to your digital license.
Windows was never activated on your device.
You reached the limit on the number of times you can reactivate Windows on your device.
Your device has more than one administrator, and a different administrator already reactivated Windows on your device.
Your device is managed by your organization and the option to reactivate Windows isn’t available. For help with reactivation, contact your organization’s support person.
I don't think that is absolutely correct. I recently had troubles with my (Dell) motherboard. I received a new one from Dell (under guarantee) After installing it, I booted up and found that activation had been completed automatically, with reference to my digital licence
But, it looks like a hit and miss affair. As my situation was a repair, I guess this statement covered it:
"Changing the motherboard, however, generates a new installation ID. Under Microsoft's licensing rules, your license is valid if you replace a motherboard because of hardware failure. You need a new license if you chose to upgrade the motherboard, because you're essentially building a new PC."
But, I read that this site (official) is still quietly working for most: