Go to office.com/setup and if you're not already signed in, select Sign in.
Note: If you bought Office for personal use through your company's Microsoft HUP benefit, you may not be able to sign in here. Find installation help at Install Office through HUP.
Sign in with the account you associated with this version of Office. This account can be a Microsoft account, or work or school account. I forgot the account I use with Office
After signing in, follow the steps that match the type of account you signed in with.