After you find Lillie and make your way through Route 3, it is time to complete your Grand Trial and battle Kahuna Hala.
Battle Kahuna Hala
After a cut scene, you can go upward and talk to Hala to battle him. If you are not ready, you can say "Please wait". If you want to visit a Pokémon Center first, go southeast from Iki Town, then when you reach Hau'oli Outskirts, go to the left to find the Pokémon Center.
Back in Iki Town, Hala has a level 14 Mankey, which has Fighting and Dark attacks; a level 14 Makuhita, which has Normal and Fighting attacks; and a level 15 Crabrawler, which has Fighting and Dark attacks. You can use Drifloon against the Makuhita, but not against the other two because Drifloon is weak against their Dark attacks. Hala can have Crabrawler use a Fighting Z-Power, All-Out Pummeling. They are all weak to Flying, Psychic, and Fairy attacks.
After the battle, Hala gives you the Z-Crystal Fightinium Z. You can give it to a pokémon that knows Fighting attacks, then use Z-Power to use a powered-up version of a Fighting attack, once per battle.
He also gives you the Melemele Trial stamp, which causes pokémon up to level 35 to obey you.
Tauros reappears, and Hala gives you a Ride Pager so you can ride Tauros. You can press Y to use the Ride Pager, then while riding, press B to dash.
Professor Kukui gives you TM54 False Swipe, which is helpful for catching pokémon.
Professor Kukui says to go visit your Mom, then go to the Marina in Hau'oli City.
Lillie asks if you will help Nebby get back to its real home.
Now that you have completed the Grand Trial, go downward from Iki Town to return to Route 1. As you go to the right, go down to the fence and you can find those rocks that Hala mentioned. Press Y to page Tauros (you can tap the circle to the left of Tauros in the list to register Tauros to the Control Pad), then while running toward the rocks, hold B to charge at the rocks and break them. The grass beyond the rocks contains pokémon that you couldn't find earlier.
Go to the left through the grass in this area to find a Nest Ball.
Go through the grass to the right, and you find a Nugget at the end.
Go down to the lower area and go to the right. This will take you to the main path. If you go upward up the path, you can use your Tauros in Route 3 to break the rocks and reach TM83 Infestation.
You can also go back into Melemele Meadow, and go downward through the flowers to reach the hole that leads to Seaward Cave. If you go downward, then toward the right, you find the northward path that is blocked by rocks. You can use Tauros to break them. At the end of the path, you find an Expert Belt.
You can also go back to Verdant Cavern, to the Trial Room in the north part of the cave, and you can go up the slope and break through the rocks to get a hidden Energy Root, and TM46 Thief.
You should also go up to where you found Nebby in Melemele Meadow, and go through the flowers to the left of there to get a Poison Barb. Go downward past the Poison Barb and you find a Poké Finder spot where you can take photos.
If you go to Route 2, there is an area on the left side blocked by rocks that you can break with Tauros, to find a Star Piece.
Then you can go back to Route 1, where you can go downward to reach your house.
After talking to Mom, if you want to explore Ten Carat Hill before you go to the next island, you can go outside your house, then go left and down to go to the Pokémon Research Lab. Go left from the lab, through the grass, and ride Tauros to break the rocks that block the path to Ten Carat Hill.
Otherwise, go to Hau'oli City Shopping District and go south to the Marina.