Windows 10 pro (not activated) Do I need to downgrade my Windows?

Hello everyone!

A Second hand HP pavilion dm4 windows 10 Pro was bought before a two months ago by my friend Which is at present Windows 10 Pro is not activated and I have searched everything to gain the product from the device but searching a lot and I can’t find it from any third party software.

WIndows 10 not activated

Since this is a second-hand laptop I cannot contact the owner where I bought it for the license key.

So my question is I want to know if I can wipe the entire drive and reinstall Windows 7 so I can upgrade to Windows 10 Home and how I would do that? Or if anyone has an easier solution.