Like, Spamhaus, Spamcop and other public real time blacklist (RBLs), you cannot simply lookup an IP at Yahoo! to see if it is blacklisted. You will need to determine the same using the bounce back message or error message at server logs like :

421 4.7.0 [TS01] Messages from <> temporarily deferred due to user complaints <> ; see
553 5.7.1 [BL21] Connections will not be accepted from, because the ip is in Spamhaus's list; see

You need to check the error code mentioned in the bounce back message. Here is the list of error codes at Yahoo!

You can request IP removal at below link:
Yahoo Sender Support Request

Note: Before you try to request removal, be sure to analyze your server to find out why you were listed in the first place. You have to fix the issue or they will just list your server again.

Do not try to get removed from the blacklist if you have not found the source of the problem.