<?php
	$arr = [100, 200, 300, 400, 500]; // An array containing some values
	$new_arr = [2 => 1001]; // Take a new array with a key where we want to keep the value
	array_splice($arr, 2, 1, $new_arr); // array_splice(old_array, position_from_where_to_start, no_of_element_of_new_array, new_array)
	print_r($arr);