How to reactivate windows 10 after free upgrade?

[Chemz11]

I'm fixing one of my family members computer. I'm suppose to activate it Windows 10. The windows 10 was acquired from the free upgrade, key wasn't given during upgrade. Previous OS was Win 8.1. What can I do to solve this?

Update: The key was changed accidentally. Looking at the asterisk censoring the key there's only a total of 5 characters, normal key has more than 5.

 

[Crixilian]

that said there is a good news on windows 10
a actived windows 10 installed on computer, microsoft will save some information like motherboard serial number or what else, so whenever you reinstall windows 10 you don't have to retype the product key

 

[Chemz11]

that said there is a good news on windows 10
a actived windows 10 installed on computer, microsoft will save some information like motherboard serial number or what else, so whenever you reinstall windows 10 you don't have to retype the product key

I
I guess I could try that, thank you