Found a DBA giving following commands at standby site to switchover while standby database was mounted.
SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY;
ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY
*
ERROR at line 1:
ORA-16139: media recovery required
SQL> recover managed standby database disconnect;
Media recovery complete.
SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY;
ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY
ERROR at line 1:
ORA-16139: media recovery required
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from another SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE FINISH;
Database altered.
SQL> ALTER DATABASE ACTIVATE STANDBY DATABASE;
Database altered.