CHANGING THE CHARACTER SET TO AL32UTF8

Open cmd as administrator.

And the following command.

# sqlplus / as sysdba

Like in below screen it's now connected.

Follow the below steps.

SQL> SHUTDOWN IMMEDIATE

SQL> STARTUP RESTRICT

SQL> ALTER DATABASE CHARACTER SET INTERNAL_USE AL32UTF8;

SQL>ALTER DATABASE CHARACTER SET AL32UTF8;

SQL> SHUTDOWN IMMEDIATE

SQL> STARTUP

SELECT value$ FROM sys.props$ WHERE name = 'NLS_CHARACTERSET' ;

Now , its set on UTF8