How to register database with RMAN recovery catalog

Replace username/password with the actuall username and password for recovery catalog; and
MYDB with the name of the recovery catalog database

1. Change SID to the database you want to register

. oraenv
ORACLE_SID

2. Connect to RMAN catalog database

rman target / catalog username/password@MYDB

3. Register database

RMAN> register database;