Your new instance first needs to know about the community. You can nudge it into the right direction by opening Search, then type in [email protected].
This might not return a result instantly - wait a few second, then search again and it should show up. From there others can find the community using a normal search, and once you (or someone else) subscribes to it, updates will be pushed to your new instance and it appears in ALL.
Keep in mind that this doesn‘t fetch older posts - you might not see any content in that specific community at first. It will however fill with new posts and comments from that point foward.
Thank you for all of your hard work! Lemmy is my very first selfhosted app and I’m impressed how easy it is spin up a new instance. It inspired me to learn coding from scratch, starting with TheOdinProject, and it’s been fun so far. Can’t wait to contribute to lemmy a few years from now :D!