Oracle Message ORA-16661 - the standby database needs to be reinstated

ERRORthe standby database needs to be reinstated
CAUSEA switchover or failover operation has caused this database to require reinstatement.
ACTIONUse the DGMGRL REINSTATE DATABASE command or Enterprise Manager to reinstate the database. If the target database has flashback enabled and it has sufficient flashback logs, the database will be reinstated as a standby database for the current primary database.