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