Step to Find APPS PASSWORD :

STEP 1 :

sqlplus> sqlplus system/system_password

sqlplus / as sysdba

STEP 2 :  (Create Function for to decrypt the encrypted password)

SQL> 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';
2 3 4 5
6 /

Function created.

STEP 3 : (Query for password)

SQL> select ENCRYPTED_FOUNDATION_PASSWORD from apps.fnd_user where USER_NAME='GUEST';

ENCRYPTED_FOUNDATION_PASSWORD
--------------------------------------------------------------------------------
ZG379C5C883FF56235BE975D075A6FD2E7A749279B7BFCE331530B443E86F41A1966E3E4B1864519
DB88BC07D58666AD837B

STEP 4: 

SQL> SELECT apps.decrypt_pin_func('GUEST/ORACLE','ZG379C5C883FF56235BE975D075A6FD2E7A749279B7BFCE331530B443E86F41A1966E3E4B1864519DB88BC07D58666AD837B') from dual;

APPS.DECRYPT_PIN_FUNC('GUEST/ORACLE','ZG379C5C883FF56235BE975D075A6FD2E7A749279B
--------------------------------------------------------------------------------
APPS

STEP 5: (Test apps password)

SQL> conn apps/APPS;

Connected.