Automated deployment between gitlab and digital ocean

Questions / Help
1

I have my elixir project up and have manually deployed it to digital ocean. Currently I every time I make changes, I have to manually go to my server and perform a git pull etc.How can i setup automated deployment such that every time I commit, the necessary mix release procedure should be done?:
currently i have setup my gitlab ci/cd configuration as follows:

image: elixir:1.12.2

stages:
  - build
  - test
  - deploy

variables:
  MIX_ENV: "prod"
  SSH_USER: "root"
  SSH_HOST: "myapp.com"
  APP_PATH: "/var/www/path_to_my_app"

before_script:
  - apt-get update && apt-get install -y openssh-client

build:
  stage: build
  script:
    - mix deps.get
    - mix compile

test:
  stage: test
  script:
    - mix test

deploy:
  stage: deploy
  script:
    - echo "$SSH_PRIVATE_KEY" | tr -d '\r' > ~/.ssh/id_rsa
    - chmod 600 ~/.ssh/id_rsa
    - ssh -o "StrictHostKeyChecking=no" $SSH_USER@$SSH_HOST "cd $APP_PATH && git pull && source .env && _build/prod/rel/my_app/bin/my_app stop && mix ecto.migrate && source .env && mix deps.get --only prod && MIX_ENV=prod mix compile && MIX_ENV=prod mix assets.deploy && mix phx.gen.release && MIX_ENV=prod mix release --overwrite && _build/prod/rel/my_app/bin/my_app daemon"
  environment:
    name: production
    url: http://myapp.com
  only:
    - main