Help Creating a Korean LoL Account pls??? (I have a KSSN)

Hey!

A korean friend lend me his KSSN to play League of Legends on the Korea server But I actually dont know how to create an account with this KSSN, because what it asks you is an i-Pin/Phone number but it doesnt give you the option to write your KSSN. Could you help me please?

Thank you so so much