In short, your tax credit for the year is divided into 12, so if you stop earning in October, you have 3 months unused tax credits and are probably due some tax back.
The easist way to do this, is to wait until the end of the year and request a end of year balancing statement, which will balance what you were paid, what tax you owe for the year and balance any over payment.
I dont know if Revenue will give a tax refund before the end of the year, as you might earn more, even if you say you are not going to. Maybe someone else can answer that definitively.
You should also make sure that you are claiming tax credits for bin collections, medical expenses etc at the same tine.