I was summoned to help collect a whimstar?

I hopped on via mobile while at work to refresh my digging progress and got a random request to help someone obtain a whimstar. Curious, I agreed. I’ve collected all but a handful of them anyway, so unless it’s one of the ones you have to chase, should be a breeze, right? I was summoned to the top of the dream warehouse and greeted by a Nikki wearing the default floating outfit (New player?) but that’s when I realized that I didn’t really understand exactly how I was supposed to help them collect stars from the open world? Helping in a Curio Domain makes sense, but just out and about, I had no idea what to do. I didn’t see a star or any indication where one may be, so I tried to chat with the Nikki to see what was up. This particular Nikki then immediately sent me back to my own realm, so ultimately it didn’t matter, but now I find myself wondering how exactly that is supposed to work?