Just done this on mine, 1.9tdi cvt (i presume its the same box)
Jack up car so you can get under it, but keep the car level.
Drain fluid from the triple hex plug and put plug back.
Pump oil in through the other plug on the bottom, a little more than you have taken out.
Use vagcom to monitor trans oil temp now
Start car and allow gearbox oil to heat to 35 deg and open the fill plug, a little oil will come out. If it carries on dripping out, then you are done. If it totally stops, then you need more oil
Something along that lines if its a 01j box
Google it, there are very in depths guides to do it