If they are laying, they need extra calcium for the egg shell. That’s all they really need, extra calcium.
There are different ways to do that. You could switch to Layer or you could keep feeding what you are and offer oyster shell on the side until that bag runs out. They seem to instinctively know which ones need the oyster shell and which ones don’t. Or just keep feeding the same stuff and always offer oyster shell on the side. That’s what I do but I almost always have young chicks in with the flock.
Another way is to switch to Layer and also offer oyster shell on the side. If all they eat is Layer, they should get enough calcium from that. But if they eat much stuff like treats other than Layer, they could come up a little short.