We can use the below API for changing the EBS(fnd_user) user password.
 
 apps.fnd_user_pkg.changepassword
 
Sample Script:
 
DECLARE
   v_user_name      VARCHAR2 (100) := 'HSINGH';
   v_new_password   VARCHAR2 (100) := :NEWPASSWORD;
   v_status         BOOLEAN := NULL;
BEGIN
   v_status := fnd_user_pkg.changepassword (v_user_name, v_new_password);
 
   COMMIT;
   DBMS_OUTPUT.put_line (
      'Password is changed successfully for the user=> ' || v_user_name);
EXCEPTION
   WHEN OTHERS
   THEN
      DBMS_OUTPUT.put_line (
            'Error encountered while restting password for user and the Error Detail is '
         || SQLERRM);
END;
 
The script can also be modified to reset bulk ebs user passworda. The below is a sample script, You need to modify as per you need.
 
Refer below syntax
 
DECLARE
   v_status   BOOLEAN;
   CURSOR user_name_list
   IS
      SELECT user_name
        FROM fnd_user
       WHERE     NVL (end_date, SYSDATE + 1) > SYSDATE
             AND user_name NOT IN ('SYSADMIN',
                                   'GUEST',
                                   'XML_USER',
                                   'APPSMGR',
                                   'PORTAL30',
                                   'PORTAL30_SSO');
BEGIN
   FOR user_name_list IN c_user
   LOOP
      BEGIN
         v_status :=
            fnd_user_pkg.ChangePassword (
               username      => user_name_list.user_name,
               newpassword   => 'welcome123');
      --  dbms_output.put_line('password successfully changed for' || user_name_list.user_name);
      EXCEPTION
         WHEN OTHERS
         THEN
            DBMS_OUTPUT.put_line (
                  'Error encountered while resetting password for users and the Error Detail is '
               || SQLERRM);
      END;
   END LOOP;
END;