http://localhost:8081/apex/apex_admin

SQL> @apxconf

      PORT
----------
      8081
Enter values below for the XDB HTTP listener port and the password for the Application Express ADMIN user.
Default values are in brackets [ ].
Press Enter to accept the default value.


================================================================================
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]
User "ADMIN" exists.
Enter ADMIN's email [ADMIN]
Enter ADMIN's password []
Changed password of instance administrator ADMIN.

Enter a port for the XDB HTTP listener [      8081]
...changing HTTP Port
SQL> SELECT DBMS_XDB.GETHTTPPORT FROM DUAL;

GETHTTPPORT
-----------
       8081

http://localhost:8081/apex/apex_admin