How to remove an Office 365 account from your Office applications.
This guide is based on Office 2019
Close all Office Apps (Word, Excel, Outlook, etc...)
Open any Office Application (e.g. Word)
From the select a template window click the link "Switch Accounts"
Then sign out of your current Office 365 account by clicking "sign out".
You will be prompted to confirm the sign out. Click “Sign Out”
Read the disclaimer and click Yes.
Close the Office Application
Reopen the application and the logged in user should be gone