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
To get it you have to get(either migrating from Pokemon ruby, sphire or emerald) regirock, registeel and regice on your team. After that, go to the mansion in snowpointcity. Go in it . When you get to the bottom, regigegus will be asleep until you activate it by pressing a on it.
First you must find your way through "SEALED CHAMBER" by diving on Route 134, after you reached Sealed Chamber you will confront the first door with Braille words, you must use "DIG". This opens an entrance to the second room.In the second room right at the front of the Braille wall you have to make Relicanth in bottom party and Wailord at the first party, then read the Braille to cause earthquake that open three gates to Regis. To find Regirock find "DESERT RUINS" in route 111 you can find it at the south of desert area in route 111 where you find TM 37(Sandstorm). Enter there and you will confront the wall with Braille words, read it, after that you must instead go two steps left, then two steps down, and then use "Rock Smash" the the door opened to your target, Regirock