Dear Naga,
Please rename
the secure storage and the workspace of dbstudio directly on file system level.
In Windows operating system the secure storage is located in C:\users\<username>\.eclipse\org.eclipse.eqinox.security,
the workspace in C:\users\<username>\sdb\databasestudio.
After relauncing the database studio, it will asks new password.
To reset control password, please check SAP note 25591.
Best regards,
James