It's all by chance. I f you FLY or BIKE, the pokemon will move/teleport. so you have to go on a long tedious journey on foot, WALKiNG... it's annoying. and they flee when you actually engage in...
Go to Jubilife City and go to the Poketch building (next to or near the Jubilife TV building). Enter through the door and talk to a man at the counter. He should give you some Poketch apps.