You would think this would be a simple 3 step process like bing or google however, following the instructions laid out by Yahoo! will bring you to one of several pages.
Following the claim listing instructions lands you on this page:
Which errors out with a partially rendered error page.
Following the create listing instructions lands you on this page:
This page also loads a partially rendered error page in the inner window.
You can simply go to https://smallbusiness.yahoo.com/dashboard/mybusinesses to manage your business listings without issues.
Why a large company like yahoo has such poor documentation on something so simple is beyond me. If someone from Yahoo! reads this please update your documentation and make use of some 301 redirects for all of these old non functioning business listing management pages.