At the north side of the route is a captain’s barricade. You won’t be able to go through until you complete the next trial, which is directly to the west. Before you go to the trial, you can surf along the ocean on the east side of the route A trainer will be swimming near the beach.
Defeat Dakota to earn P456. Continue surfing to the northeast to find a mini island. Unfortunately, you won’t be able to access it from the south. Surf along the ocean to the north until you reach another beach to the northwest. Another Zygarde Cell will be along the shore. This beach area will have Pokemon scurrying from one den to another. Intercept these dust clouds to start a battle with wild Diglett.
Continue along the shore to the north up onto a small cliff. A Max Repel can be found here. Jump back onto Lapras and surf into the ocean to the east. Another Trainer can be found swimming around.
Defeat Tiare to receive P456. Surf east and look below the surface of the water to find a slightly hidden Antidote. This item will be near another swimming Trainer.
Defeat Casey to receive P456. Surf south to finally reach the mini island. Another Trainer will be near the north end of this island.
Defeat Vanessa to earn P456. To the south is a small pond to fish at, and to the left of the pond is TM73 Thunder Wave. You can jump over the ledge to the southwest to quickly return to the mainland of Route 7. Now that the route has been completely explored, head to Wela Volcano Park to start the next trial.