How to Restore spfile from backup

1.Connect to target Database with RMAN.

i)If you have lost your spfile while your database is running then,

RMAN>CONNECT TARGET /

ii)If your database is not up and you don't use recovery catalog then use,
RMAN>CONNECT TARGET /
RMAN>SET DBID 3386862614

2)Start the instance with dummy parameter file.
RMAN>STARTUP FORCE NOMOUNT

3)Restore server parameter file.
To restore in default location,
RMAN> RESTORE SPFILE FROM AUTOBACKUP;
To restore in another location,
RMAN> RESTORE SPFILE TO 'new_location' FROM AUTOBACKUP;

If you want to restore to a pfile then use,
RMAN> RESTORE SPFILE TO PFILE '/tmp/initTEMP.ora';

4)Start the instance.
RMAN>STARTUP;