If you have already opened the cave's to all 3 regi's then this but if you did not I would
reccomend you look on youtube for help walkthrough will be easy enough to catch I know how
to catch regice and regirock but not registeel

now let's start with regice start  at petalburg for dewford head to route 105 look on
you're howen map if you don't know where that is go to the island that reach's to the
other side of the sea go staight until you see an opening to a small cave go inside the
cave look at writing from that spot stay on the walls and go in a complete circle around
the walls and back to the writing the door will open go inside and you will see regice
bring alot of ultra balls but before you fight save so that you will not have to start all
over from the beginning if you wan't to catch him on the first battle then bring a master
ball

now for regirock but before I tell you about regirock bring at least 2 master ball's so
that you will be ready for both regirock and registeel now let's start go straight to the
desert and go all the way to the end of the desert until you reach the cave to regirock go
straight to the writing and take a quick look at it after you're done go two space's down
and go two space's left and the door will open now face regirock with your master ball and
throw it at him if you don't have a master ball bring alot of ultra ball's and maybe some
timer ball's be patient and lower his health at the peak of his health keep throwing ultra
ball's untill you got him

that's it for now sigh!!