Oracle forgot user name and password

Microsoft Windows [version 10.0.16299.192]
(c) Microsoft Corporation. All rights reserved.

C:\windows\system32>echo%oracle_sid%
%oracle_sid%

C:\windows\system32>set Oracle_sid=fast

C:\windows\system32>sqlplus/as SYSDBA

Sql*plus:release 12.1.0.2.0 Production on Friday February 2 17:03:37 2018

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

Connect to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0-64bit Production
With the partitioning, OLAP, Advanced Analytics and Real application testing options

sql> alter user fast identified by "fast*123";
Alter user fast identified by "fast*123"
*
An error occurred on line 1th:
ORA-01918: User ' FAST ' does not exist

sql> alter user SYS identified by fast*123;
ALTER user SYS identified by fast*123
*
An error occurred on line 1th:
ORA-00922: Missing or invalid option

sql> alter user SYS identified by fast*123;
ALTER user SYS identified by fast*123
*
An error occurred on line 1th:
ORA-00922: Missing or invalid option

sql> alter user SYS identified by "fast*123";

The user has changed.

sql> alter user system identified by "manager";

The user has changed.

Sql> create user fast identified by "fast*123";
Create user fast identified by "fast*123"
*
An error occurred on line 1th:
ORA-65096: Invalid public user name or role name

sql> Create User "C # #fast" identified by "fast*123";

The user has created.

Sql> Grant CONNECT,RESOURCE,DBA to "C # #fast"
2
Sql> Grant CONNECT,RESOURCE,DBA to "C # #fast";

Authorization is successful.

Sql> commit;

Submit complete.

Sql>

Oracle forgot user name and password