Follow these steps found in their FAQ: http://subscriber.zoominfo.com/usercenter/index.php/pro-faq#removal or if you’re a daredevil, try the direct deletion link.
Otherwise, contact them: http://www.zoominfo.com/business/about/contact-us
URLS:
http://www.zoominfo.com/
http://www.zoominfo.com/lookupEmail
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.