Hi!
Which version of Office are you licensed for?
Did you set up your computer yourself, or did someone else set it up for you?
Did Office come pre-installed, or did you install it yourself?
Is this the same Gmail account you use for Office and your main Windows installation?
Have you tried a different verification method? Besides the PIN, you can use your password. Click on "Sign-in options" and select the password option.
The PIN is specific to each computer, so changing it on another device won't work.