Please Bring down the WF mailer and take proper backup before performing the below steps.
1) You need to update the notifications you do not want to sent, in the WF_NOTIFICATIONS table.
SQL> select notification_id,status,mail_status,begin_date from WF_NOTIFICATIONS where status = 'OPEN' and mail_status = 'MAIL';
2) To update a notification so that it will not get e-mailed. Set the MAIL_STATUS = 'SENT'. The mailer will think the e-mail has already been sent and it will not send it again.
SQL> update WF_NOTIFICATIONS set mail_status = 'SENT' where mail_status = 'MAIL';
3) Then run the script wfntfqup.sql to purge the WF_NOTIFICATION_OUT queue and rebuild it with data currently in the WF_NOTIFICATIONS table. This is what purges all notifications waiting in the queue to be sent. Only the ones where mail_status = 'MAIL' and status = 'OPEN' will be placed in the WF_NOTIFICATION_OUT queue and sent by the mailer.
SQL>sqlplus apps/apps_pwd @$FND_TOP/patch/115/sql/wfntfqup APPS APPS_PWD APPLSYS