Accessing postgres that is hosted on Heroku

So I've deployed my project into Heroku using Gitlab CI/CD using following file:

image: maven:3.8.6-openjdk-18

services:
  - postgres:latest
variables:
  POSTGRES_DB: postgres
  POSTGRES_USER: postgres
  POSTGRES_PASSWORD: password
  POSTGRES_HOST_AUTH_METHOD: trust

stages:
  - build
  - deploy

build:
  stage: build
  script:
    - mvn package -Pprod
  artifacts:
    paths:
      - target/cinema.jar

deploy:
  stage: deploy
  image: ruby:latest
  script:
    - apt-get update -qy
    - apt-get install -y ruby-dev
    - gem install dpl
    - dpl --provider=heroku --app=cinema --api-key=$HEROKU_API_KEY
  only:
    - main

I would love to connect from this place to postgres and give user all of the needed privileges on all tables to provided user.

Can't wrap my head around it, in order to make it work.

Thank you for any help!