i think there is some misunderstanding here in how the Bash script comes into your task container.
Thats the local path under which your bash script resides on your computer. But Concourse instead runs your tasks in a docker container.
For the docker container to be able to execute the script, it first needs to mount the resources that are required for this.
In the Concourse world this is done via Concourse Resources. In your case, you could e.g. put your Bash script into a Github Repo and let Concourse receive it from there using the Concourse-Git-Resource.
To see how you can work with resources and reference them in your Jobs and Tasks checkout this tutorial Pipeline-Resources.