it is simple. stop playing and go outside
After you beat the league you go to the snow point temple.
you have to migrate the 3 regis and then have them in your party and go to the snow point temple and then just talk to the statue
snow point temple in snow point city its at the top of the town map
in the temple in snow point
Regigigas
Snow point temple
deafeat Cynthia and get the national dex go to snow point city and talk to the protecter of the temple and he'll say you can go inside! great tip!:if you go in the temple with:Regice,Regirock and Registeel you can have the chance to catch the ledondary Regigigas!Be carefull though you should go easy on him because he is only lv 1
you go to the snow point temple with the other regias they awaken reggias who wich was asleep
you get reggigas when you get reggirock, reggisteal, and reggice and go back to snow point temple to the reggigas statue and battle him
you can catch regigigas in the snow point temple
snow point temple
regigas or how ever you spell it <(^(oo)^)> >`.`)>