First look for pg_hba.conf , you can use locate command to do so
locate pg_hba.conf
Then edit the file on your favorite editor
vi /var/lib/pgsql/9.6/data/pg_hba.conf
Add the following line to the file
host all all 192.168.0.1/32 md5
In order to apply changes, you must reload the service. In my case, I have pg version 9.6 so commands will be
service postgresql-9.6 reload
service postgresql-9.6 status