Get Zapdos, Moltress and Articuno without cheating in Pokemon Platinum

Go to Eterna Town and head to the very bottom house. Go into the house and talk to Professor Oak. He will say the three legendary birds are in Sinno.
Go to the app. Legendary finder put a shape on where you first see Crysallyer and walk around.
Look at your app. and 3 Pokemon are wondering around Sinno