To post an update chapter or not?

So I have a finished fic, (2-shot). And after thinking about the universe have decided to make it into a series. However when I completed the story it wasn’t in a series so people could only subscribe/bookmark the work and not the series. Should I post another chapter when I post the new fic letting people that subscribed to the work know there’s more? For context the work has 55 subscriptions and 119 bookmarks…