Reset DBID

Reset database id so that it can be backed up if the same DBID already exists in RMAN catalog
for a different database.

SVRMGR> alter database backup controlfile to trace resetlogs;

SVRMGR> shutdown immediate;

SVRMGR> startup mount;

SVRMGR> select dbid , name from v$database ;

DBID       NAME
---------- ---------
 673658548 MYDB

SVRMGR> execute dbms_backup_restore.zeroDbid(0);

SVRMGR> shutdown normal;

Rename the trace file to rename_db.sql

Edit file rename_db.sql remove comments and extra stuff and replcate 

REUSE DATABASE 

with the following

REUSE SET DATABASE

SVRMGR> connect internal;

SVRMGR> @ /apps/oracle/admin/MYDB/udump/rename_db.sql

SVRMGR> select dbid , name from v$database ;

 DBID       NAME
 ---------- ---------
 1921805231 MYDB