If you remember your PIN and want to change it: Just click on "Change" If you don't remember then send a ticket.
I made a new account but where can i login? When i lounch the game it goes straight to the account wich i dont know the Pin.
Well the new Steam system only makes posible 1 login per Steam account. So just log in another Steam account or you can also download the game from here, download and install it. It will ask always a login info.