until and rangeTo operators that can be replaced with Collection.indices or iteration over collection inside for loop.
Using syntactic sugar makes your code simpler.
The quick-fix replaces the manual range with the corresponding construction.
Example:
fun main(args: Array<String>) {
for (index in 0..args.size - 1) {
println(args[index])
}
}
After the quick-fix is applied:
fun main(args: Array<String>) {
for (element in args) {
println(element)
}
}