I have used omibus. Gitlab.rb is a big file and all lines are comment .Its a fresh install. I have configured only this part rest are in comment

Disable the built-in Postgres

postgresql[‘enable’] = false

Fill in the connection details for database.yml

gitlab_rails[‘db_adapter’] = ‘postgresql’
gitlab_rails[‘db_encoding’] = ‘utf8’
gitlab_rails[‘db_host’] = ‘10.33.255.146’
gitlab_rails[‘db_port’] = 5432
gitlab_rails[‘db_username’] = ‘gitlab’
gitlab_rails[‘db_password’] = ‘gitlab’

Suppose my Omnibus git install v 12.10.3 whose IP 10.x.x.A
postgresql ip 10.x.x.B
PostgreSQL
11.8 (Ubuntu 11.8-1.pgdg18.04+1)
PostgreSQL JDBC Driver
42.1.1

DB: gitlabhq_production
user: gitlab
user: gitlab