You mean after beating Tundra Admin Royce? Go to Amethyst City and battle your rival near the gym. He'll give you a Card Key. Go east to the Sewage Treatment Plant to fix the power outage. Keep going east in Amethyst Sewers until you enter the generator room. Battle against Tundra Admin Krystal then go back to Amethyst and now you can go to the gym. :D
Well, you said we should ask you regarding of azure horizont beta2...
So where are you supposed to go after you beat the evil team(can't remember the name) in their hideout after the second gym battle...?