If you are Nightcrawler of the Cavaliers, go to South Hart and play with 30 mission props at the training ground.
If you are an adventurer's flash, go to a bar in Du Fei to find Dacrewe (it seems to be called this, it is an instructor with a flash turn) to pick up the task, and go to the north gate of Du Fei-Duffy North Factory to find an instructor with a flash turn. He will send you to a place, hit the monsters there, explode 30 black beads in that map to the instructor who flashes twice, and then go to Dacrewe.