Hi, Renz. I'll be happy to assist you today.
Sorry to know you're experiencing this Windows activation issue.
Unfortunately, there is not a way to get oficial free Windows activation code. In your case, I recommend you this: if the computer comes with Windows preinstalled, please install the same Windows version again. This will allow you to activate Windows correctly.
From the following link, you can get the Windows media creation tool which will allow you to create the media. This url also provide the required steps to install Windows.
https://www.microsoft.com/en-us/software-download/
If you need anything else, please let me know.