How to increment value of a parameter in a function?

Im getting an error of val cannot be reassigned inside function b even though I initialized the parameter as val in function main.

fun main () { var counter = 0 val checker = readln()

functionB (counter, checker) }

fun functionB(counter :Int, checker: Int) {

if (checker == 5 || checker == 8) { counter++ } else {println(“Not counted”}

}

I need the variable counter in the main function increase by 1 whenever user inputs 5 or 8.