Go through microsoft365.com/setup webpage, Sign in, and enter the product key to download and install Microsoft 365 or Office on your computer.

Go to Microsoft365.com/setup, Microsoft 365 Setup website.
Sign In to your Office Account or Create a New One.
Now Enter Product Key.
Click Install Office Button.
Go ahead and Click Install Office Again.
Save and Run office setup.
Wait for Office to finish Installation.
Click Close, Installation is finished.

Greetings,
Peter