Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
You won't need a product key, you need to deactivate your previous Installation and then re-install Office 365
On your computer, go to https://office.com/myaccount and sign in using your Microsoft account, if prompted
Select Install
Under Install information, locate the old installation.
Select Deactivate Install to deactivate the Office installation
Then, click Install to install Office
Transfer / Stuff you can Do in MyAccount: Install / Deactivate / Offline Installer / Downgrade
https://answers.microsoft.com/en-us/msoffice/wi...
log in to the MyAccount site http://office.com/myaccount
This page shows how to install Office AFTER the license has been activated. It also shows a few other things you can do in the MyAccount site.