Can I install on existing Docker?

Well I tried that but end up with this error:

Error: {"message":"No such image: discourse/discourse"}

I think it’s on the end of the Plesk extension. At the end of the day with Docker i’m just a button pusher so I will have to try to plow through configuring Discourse using the git repo + the Docker extension in Plesk so I can manage it from the control panel. I had Discourse setup in under 30 minutes before I updated my server so if this becomes bigger than I can handle I guess I’ll go old school with it. Thanks for your response.