How do I subscribe to a community outside my instance?

Hi. I've subscribed to several communities outside my instance already, but I'm having a problem where I can't seem to repeat the process for certain communities.

For example, I wanted to go to /c/test on lemmy.ml. But going to lemmy.ml/c/test takes me outside of Beehaw, my home instance, so I can't post or subscribe from there. So I checked how I could visit this community, and its URL is https://beehaw.org/c/lemmy_support@lemmy.ml. I then tried going to https://beehaw.org/c/test@lemmy.ml, but that gives me an error page.

What do? I can't find /c/test on the communities page, either.

Apologies if I'm being dumb.