After you complete Captain Ilima's trial in Verdant Cavern, Professor Kukui asks you to look for Lillie in Route 3.
In Route 3, if a shadow flies over your head, you might get attacked by a flying pokémon.
In the northern part of the route, you can battle Rising Star Ian. He has a level 12 Psyduck. You get 576 Pokédollars for winning.
If you go through the grass near Ian, there is a Heal Ball to the right.
If you go up the southern part of the route, where some shadows of flying pokémon are going around, there is a Sharp Beak next to the rock if you go through the southernmost path.
At the top of the northernmost path, you can battle Rising Star Tatiana. She has a level 12 Cottonee. You get 576 Pokédollars for winning.
At the top of the hill, you find a sign next to a cave entrance. It goes to Melemele Meadow. Go inside.
In the cave, you find Lillie, who is looking for Nebby.
First, go downward and follow the downward path until you find a Great Ball.
You can walk down into the flowers. Rotom will give you a temporary boost to increase the Exp. Points you earn in battle. You will encounter wild pokémon in the flowers. If you see sparkles in the flowers, check on them to get Nectar. Go to the left and go up the ramp to get the Net Ball on the ledge.
If you go downward through the flowers, you find a hole in the wall to the left. You can check on it to go into Seaward Cave. You find an Escape Rope there.
Go farther downward and you see Nebby, and then you must battle Ultra Recon Squad Dulse (in Ultra Sun) or Ultra Recon Squad Soliera (in Ultra Moon), who has a level 13 Furfrou. You get 156 Pokédollars for winning.
After the battle, there is a cut scene where the Ultra Recon Squad mentions Megalo Tower.
After the Ultra Recon Squad leaves leave, talk to Nebby and you will go together to meet Lillie. Lillie will heal your pokémon, then the two of you will go outside. Hau will battle you. He has a level 13 starter (Popplio if you chose Rowlet, Rowlet if you chose Litten, Litten if you chose Popplio), a Noibat, and a level 12 Pikachu. You get 240 Pokédollars for winning.
Afterward, Professor Kukui tells you that now that you have finished your trial, you need to battle Kahuna Hala to complete your grand trial.
Now you can return to Melemele Meadow to explore, or you can continue through Route 3.
If you want to continue through Route 3, go south from the entrance to Melemele Meadow, and you will find a bridge. Before you cross it, go to the right and talk to the man to get a Soothe Bell.
Now go to the left and then go down across the bridge. You can fight Rising Star Joshua, who has a level 12 Growlithe. You get 576 Pokédollars for winning.
Farther down the path, you find a Super Potion.
Go back upward, across the bridge, and talk to the Ace Trainer near the entrance to Melemele Meadow. If you have defeated all of the other trainers on Route 3, you can battle him if you wish. He is Ace Trainer Makana, and he has a Butterfree and a level 14 Slowpoke. You get 952 Pokédollars for winning. He will give you TM19 Roost after the battle.
Now go farther south. You will see some grass to the right. Beyond it, there are some berries. To the right of where you found the berries, there is a Nest Ball.
Go downward from the grass and talk to the guy. If you agree to help him, he asks you to catch a Sableye, which can be found in Ten Carat Hill, and show him your Pokédex afterward. He will pay you if you do.
Then go south and you will reach Route 1. Go left from there and go up the stairs to reach Iki Town.