Well actually each DSI has a different master key because of the inquiry no.So call NINTENDO support line and tell them your DSI's inquiry no.
What Are The 5 Digits Of The Dsi Master Key?
Its hard to say if you contact nintendo you are going to have to give proof of id like the dsi serial code well like he said each ones got a different code if your a kid like me trying to figure this out get your parents to call nintendo srry thats all I can help with
I think you have to call the phone number on the manual and then you ask for the master key for dsi because you forgot the parental control pin...so yeah hope this helped.