lex and yacc add support for one feature in existing parser code (C)

Hello,
I have a pasrer in lex and yacc for a specific language.
I need to add support for "arg->" and change the function declaration order from:
function int foo(){
to:
function foo(arg-> x, y, z: int; arg-> f: real): void{
function goo(): char{
I need it now, within few hours, if you are not experienced don`t contact me. its 5 minutes work.