How to clean up defined answers for Challenge Questions in OIM?

Hi, we're using Identity Management Suite 11gR1 PS1.   We deployed an application to allow users to set answers to some predefined challenge questions, so that they can reset passwords by answering these questions in case they forget the original password.

Around 150 users have their answers defined since production.  Now we're requested to change the challenge questions.     We managed to update the application to use new set of challenge questions but no idea how to clean up already defined answers.    We're using standard classes:

import oracle.iam.identity.usermgmt.vo.User;

import oracle.iam.passwordmgmt.api.ChallengeResponseService;

import oracle.iam.passwordmgmt.vo.Challenge;