To uninstall Office for Mac 2011 move the applications to the Trash. Once you've removed everything, empty the Trash and restart your Mac to complete the process.
Before you remove Office for Mac 2011, quit all Office applications and make sure there's nothing in Trash that you want to keep. Leave Microsoft 365 applications closed while you go through this process.
Note: You must be signed in as administrator to do these steps, and you probably already are, if you're using your own Mac. If you're at a Mac that's part of a network at work, you might have to ask someone in your IT organization for help with signing in as administrator.
Remove the Microsoft Office 2011 folder
Open Finder > Applications
Find and then drag the Microsoft Office 2011 folder to Trash.
Restart your computer.