Is it Outlook email at Outlook.com or the Outlook app in MS Office 365?
Hubby is running Outlook 365 on Windows 10 and has had some issues with it randomly not launching for about a week. (I’m SO glad I gave him that POS Windows 10 that used to be mine.)
When in Outlook, you should be able to go under File > Account Settings, and click on Account Settings. Then look at the “Email” tab. You should be able to see and remove the previous user’s account from Outlook. Alternately, you can completely uninstall the Microsoft Office suite in its entirety - but just removing the email account from Outlook is a lot easier.
Start Outlook in Administrator mode (Right click shortcut select “Run As”) and the option should work.