Start the Managed recovery process (MRP) on standby server - ORACLE DATAGUARD

 
What is MRP in Oracle database?
Managed recovery process (MRP) The managed recovery process (MRP) applies information from the archived redo logs to the standby database. 
When performing managed recovery operations, log apply services automatically apply archived redo logs to maintain transactional synchronization with the primary database.

Start the apply process on standby server.

# Foreground redo apply. Session never returns until cancel. 
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE;

# Background redo apply. Control is returned to the session once the apply process is started.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;

If you need to cancel the apply process, issue the following command.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

If you prefer, you can set a delay between the arrival of the archived redo log and it being applied on the standby server using the following commands.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DELAY 30 DISCONNECT FROM SESSION;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE NODELAY DISCONNECT FROM SESSION;

Provided you have configured standby redo logs, you can start real-time apply using the following command.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT FROM SESSION;