Piggy proposes to move the fire to the beach, away from the mountain, to avoid it going out and losing the chance of being rescued. He believes the fire is more useful and visible on the beach as a signal for passing ships or planes.
Piggy is the voice of reason in chapter 2 because he insists that they make a fire so they can be rescued. Also in this chapter they use his glasses to light the fire.
one of the little kids was not there and he thinks he was caught in the forest fire.
By Piggy's glasses and the sun reflecting off them
In chapter 2 of Lord of the Flies, the boys start the fire by using Piggy's glasses to focus the sun's rays onto dry leaves and twigs. This method allows them to create a flame and start the fire for a signal to potential rescuers.
Because in the end of the chapter, Jack's tribe attacks Ralphs tribe. Piggy thought they were after the conch (The Shell) but instead, they stole Piggy's glasses for fire usage (The Glasses)
Well in chapter 10 Jack and his tribe of savages invade Ralph's tribe (made of up Ralph, Sam and Eric, Piggy, and one/two littluns) in order to steal Piggy's glasses, which is overall the power to start a fire on the island. Jack might have mentioned this plan in chapter 9 so I'm hoping this is the right answer to your question.
Piggy suggests using his glasses to start a fire by focusing the sunlight, rather than relying on the unreliable matches. He believes this method will be more efficient and effective in ensuring their rescue.
In "Lord of the Flies," Piggy's glasses are taken in chapter 2, on page 40 in the 1999 Penguin Books edition. The boys take Piggy's glasses to start a fire.
Ralph said that near the end of chapter 2: Fire on the mounatin when Piggy admitted that he didn't know the names of the littluns.
Jack damages them once screwing with the fire
one of the little kids was not there and he thinks he was caught in the forest fire.
When Jack accused Piggy of not helping much with the building of the fire in chapter2: Fire on the Mountain Simon defended Piggy by mentioning that they had used Piggy's spectacles to light the fire so he had helped in that way.