Do your instructions apply only to Google Chrome browser?
My understanding is Google collects information on any Google search engine request regardless of browser, that is, Internet Explorer or Firefox users history is collected regardless of their history privacy settings. Right?
You'll want to use Chrome to get into the Google MyActivity link and delete your Google Search History. Note: The links I posted are NOT the simple "delete your browser cache" ...these are the links Google provides that enable you as a user to delete your Google Search History that they store on their servers.
NOT your browser.