how to recover internal user & password in oracle apex 18.2

Microsoft Windows [Version 10.0.17134.523]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\Users\Quium>cd..

C:\Users> cd..

C:\>cd C:\Apex\apex_18.2\apex

C:\Apex\apex_18.2\apex>sqlplus

SQL*Plus: Release 12.2.0.1.0 Production on Tue Mar 12 10:25:18 2019

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Enter user-name: sys as sysdba
Enter password:

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> @apxchpwd.sql
...set_appun.sql
================================================================================
This script can be used to change the password of an Application Express
instance administrator. If the user does not yet exist, a user record will be
created.
================================================================================
Enter the administrator's username [ADMIN] admin
User "admin" does not yet exist and will be created.
Enter admin's email [admin] quium@gmail.com
Enter admin's password [] Enter your password
Created instance administrator ADMIN.