Find Bonsly on the ship in the desert. He will run from you. You need to put some food at the oasis Poke Spot. After awhile he will come to it. Then, go back to the old man. He will give a Battle Bingo card with Bonsly on it. Take it to the Battle Bingo place. Go into your pad and it will have the flash this card option. Pay 500 Poke Dollars to battle with Bonsly.