fun main() {

    //define a list of 3-letter months from Jan to Jun
    val months = listOf("Jan", "Feb", "Mar", "Apr", "May", "Jun")
    //put "May" as the first element of the list
    val months2 = months.toMutableList()
    months2.add(0, months2.removeAt(4))

    println(months2)

}

Output

[May, Jan, Feb, Mar, Apr, Jun]