If your primary is not available and you want to convert your standby database into Primary manually then use the below steps on the standby database.
SQL> select open_mode,database_role from v$database;
OPEN_MODE DATABASE_ROLE
-------------------- ----------------
READ ONLY PHYSICAL STANDBY
SQL> recover managed standby database cancel;
ORA-16136: Managed Standby Recovery not active
SQL>
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE FINISH;
Database altered.
SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY WITH SESSION SHUTDOWN;
Database altered.
SQL> select open_mode,database_role from v$database;
OPEN_MODE DATABASE_ROLE
-------------------- ----------------
MOUNTED PRIMARY
SQL> alter database open;
Database altered.
SQL> select open_mode,database_role from v$database;
OPEN_MODE DATABASE_ROLE
-------------------- ----------------
READ WRITE PRIMARY