The easiest way is to go to your instance’s search bar and look up “!jerboa@lemmy.ml”, in the case of this community. This should make it show up even if it wasn’t added to the instances “index” (I’m also new here idk the terminology all that well), as long as both instances are federated, which they most likely are. But yeah it doesn’t work on Jerboa yet. I used that to subscribe to the communities I wanted