u cant
There was the same question further up, but, you have to have a Pokemon who's mirage number matches the day's mirage number of the Island. Sorry, I don't know who orignally answered it...but credit to them.
ask the man looking out da window in pacifidlog if he says he sees mirage island go surf east til u find a piece of land u have 2 b lucky
Answer;In pacifidilog town, there is a man looking outside a window, every time you ask if he can see mirage island he says no right? Well I still can't do it but from what I've heard, you have to have a Pokemon's 'number' (kinda like a credit card or birth number, though Pokemon problably hav neither,) to the number of which the game randomly pulls out every what ever or so. Well, sorry, but that's all I know, and considering I haven't done it myself, I can't prove this either.