Postgres Replication Switchback to master in Postgres-9.6

Hi Team

I have setup the Postgres Hot Standby with streaming replication with help of pg_basebackup
I need a help on switback to old master as master server.

Switchover on Failover
On Failover I am able to make Standby to become primary and continue with command "pg_ctl promot"
Found it is easy process

Switchback
Case, want to switch back old master as Master server and move the new Master one as Standby Server.

- Master is down

- Promoted slave as master

- Inserted few records

- Need to demote the Slave and bring back the Master
What is the correct procedure to sync data between Slave and newly started Master
Is it same process should follow while creating standby?

Thanks in advance, your reply will greatly help.

Thanks and Regards
Ramaswamy B.A

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