I'm trying to pass parameters by reference from C++ to a function written in assembly, but I can't seem to actually change the value within the assembly function. What am I doing wrong here?

void __declspec(naked) asmChange(int&){
  __asm{
    mov   [esp+4], 5
    ret
  }
}

int main (){
  int a = 12;
  cout << "Before: " << a << endl;
  asmChange(a);
  cout << "After: " << a << endl;
  return 0;
}

In the program above I'm simply trying to change the value of a variable. I don't really understand what I'm doing wrong here and can't seem to find any answers to my issue anywhere else online.