A family of Microsoft word processing software products for creating web, email, and print documents.
> the most simplest way possible
I can't say this will be the simplest way, but I think you should be able to do it.
Go to BibWord
https://github.com/codingo/BibWord
Click on the Styles folder at the top of the page.
Next, choose the Harvard style you want.
When the file opens, click the download icon in top right corner:
Copy the file to where Word stores its style files. For Windows this is usually at:
%appdata%\Microsoft\Bibliography\Style\
Finally, close Word and reopen it. The Harvard style should now be there.