1- shutdown abort
2- copy one of the good copies of the control file to the location of the corrupted or missings control file.
if the corrupted Cfile resided on a failed disk , copy it to another suitable location and update the initialization parameter to update the cfile reference or you can remove the reference from this initialization parameter until you find a suitable location.
you must have at least two control files in your Db.
3-start the instance with startup.
you´ll change the initialization parameter control_file using the alter system set scope=spfile when the instance is started in no mount mode.
