How to add output_dir to app platform app

Hey guys, currently im trying to deploy a symfony app on the app platform, so far i’m able to get the application to deploy but when i got to the active webpage i get a 403, this is due to the server looking wihtin the / of my project rather than /public where my assets are, i’ve had a google and it seems all i need to do is define the root and the define the output_dir to be my built assets dir

Below is my config, i have been unable to find the correct format for this, i also seem to have also found a post somewhere in the community forms here saying there should be an output directory input field upon creating the services but am unable to see where that is.

Thanks!

alerts:
- rule: DEPLOYMENT_FAILED
- rule: DOMAIN_FAILED
databases:
- engine: PG
  name: db
  version: "12"
envs:
- key: APP_ENV
  scope: RUN_AND_BUILD_TIME
  value: dev
features:
- buildpack-stack=ubuntu-22
ingress:
  rules:
  - component:
      name: vectisplanner
    match:
      path:
        prefix: /
name: vectisplanner
region: lon
services:
- build_command: |
    composer update
    composer install
    npm run build
  environment_slug: php
  envs:
  - key: DATABASE_URL
    scope: RUN_TIME
    value: ${db.DATABASE_URL}
  github:
    branch: main
    deploy_on_push: true
    repo: Wordlesschunk/VectisPlanner
  http_port: 8080
  instance_count: 1
  instance_size_slug: basic-xs
  name: vectisplanner
  run_command: heroku-php-apache2
  source_dir: /

the application is working if i go to https://blah.com/public