forgot apps password

Hi

Could you please share me your advice on the following issue.

EBSR12.2.6 Database 12.1.0.2 environment.

We forgot apps password,Could you tell me the method to retrieve the password. I have tried the following method

1) Login as sysdba

2) create FUNCTION apps.decrypt_pin_func(in_chr_key IN VARCHAR2,in_chr_encrypted_pin IN VARCHAR2) RETURN VARCHAR2 AS LANGUAGE JAVA NAME 'oracle.apps.fnd.security.WebSessionManagerProc.decrypt(java.lang.String,java.lang.String) return java.lang.String';

3) select ENCRYPTED_FOUNDATION_PASSWORD from apps.fnd_user where USER_NAME='GUEST';

4) SELECT apps.decrypt_pin_func('GUEST/ORACLE','') from dual;

it didn't work.The step 4 returned null.