If you have a new device that came pre-installed with Office 2021 and after opening an app you see a message that says Office needs an update, you'll need to do this before you can continue using Office.
To update Office, do the following.
From an Office app, such as Word and in the backstage area of the app, select Account.
Under Product Information, choose Update Options > Update Now.
Close the "You're up to date!" window after Office is done installing updates.