Do you know which VAS tool I need to purchase for a 2013 Audi A4?
Hello and welcome to just answer.
You do require a diagnostic machine to reset your light and you will need to buy one that covers all control units on your car.
There are various machines on the market and some will cost a lot of money. A good garage should have a machine capable of reseting the light for you.
However if they don't one of the best pieces of equipment to get is called VAG-COM or VCDS. This is used on your laptop with a cable that connects to your car. This software will allow you to pretty much do anything on your car that an Audi garage can do.
I hope this helps and if I can help further please feel free to ask