I'm going to assume/speculate, that this will heavily be about Team Rocket, and the usual gang will have a minor role in this episode (in context to Meltan), because otherwise I feel like the following episode's title would inherently contradict this episode's existence. Which is why I have to assume this is a two parter in the way where Ash and company barely interact with Meltan than Team Rocket.
Because otherwise it'll be strange, to interact with Meltan for a decent chunk of time, but then SUDDENLY the next episode is "A New Species Has Been Discovered?" because if the group (including Kukui maybe) had any meaningful interaction with Meltan in this episode, why wouldn't the "New Species" aspect be relevant to the title in this episode?
I mean sure there's the whole (possible), the titles have done that before, where the first episode doesn't indicate vital importance that the 2nd/two parter episode would more accurately convey. I just think it would make more sense to have Ash and Company having a minor role with Meltan, but go to great lengths to saving Meltan, and that's the episode, and then at the end "What is this thing?" leading to the next episode.
It'll be weird and chaotic, if they are trying to figure out what it is IN this episode for a good chunk of the episode, but Team Rocket "plot" gets in the way, and that at the end they are still wondering what Meltan is following up the next episode. It is possible, I just would find it more weird than just having Meltan be a rare "appearance" for Ash and Company, knowing it exists, maybe trying to find it, Team Rocket plot happens, Ash and Company rescue Meltan only for them to be like "So what is this thing actually?" which makes more sense to me.
Though I guess its possible, they are interacting with it for the beginning of the episode. James freaks out about what it did, and it gets abducted or goes missing, Ash and company save it, and that takes up most of the episode, leading up to follow up episode.
Well it'll be awhile, so I guess we'll wait for a preview, to see just how its interacting with the group, or what the preview shows.