in the case of discourse to add its docker image to a service you would input discourse/base:release into the input field when prompt to select an image, for a pre-existing service, you can do this by going into the settings under the source section

Thank you @Brody , discourse/base:release did work for the image name, it's deployed!
Would there be a way now to run ./discourse-setup on that image, according to this guide:
https://github.com/discourse/discourse/blob/main/docs/INSTALL-cloud.md#6-edit-discourse-configuration

id say youd want to run that command locally through the railway cli

thanks again @Brody , I connected to the project's service through the railway CLI on a local clone of discourse_docker repo and ran:
railway run sudo ./discourse-setup
(sudo was needed)
The result was:

Password:
./discourse-setup: line 149: free: command not found
./discourse-setup: line 180: [: : integer expression expected
./discourse-setup: line 189: [: : integer expression expected
Ports 80 and 443 are free for use
samples/standalone.yml -> containers/app.yml
./discourse-setup: line 149: free: command not found
Found GB of memory and 8 physical CPU cores
./discourse-setup: line 260: [: : integer expression expected
./discourse-setup: line 264: [: : integer expression expected
./discourse-setup: line 268: 256 * : syntax error: operand expected (error token is " ")

Hostname for your Discourse? [discourse.example.com]:

I guess there are some issues, but the prompt for generating the yml shows up. I confirmed enough for now, thank you for reaching out!

you would need to have a local install of discourse and all of its cli tools, since railway run runs the command locally but with the railway service variables available

Did you manage to install your Discourse forum in Railway service?