How do you add transmission fluid to 1996 passat?

Have a look under the trans pan. There are two hex bolts. One is 17mm (that's for filling), the other is 8mm (that's for draining). Fill using an oil pump ($5 from SuperCheap) until the oil flows out. Then start the engine (which will drop the level as the trans takes up oil into valve body) and continue filling until it runs out again. Leave engine running, jump in car and change between each gear holding each gear for 3 seconds (This allows the galleries to fill). Get under and fill again until oil drips out. Lock down the 17mm filler bolt and turn engine off. 2-3 days later, check the level again.

More info from here http://www.taligentx.com/passat/maintenance/atfchange/

Good luck.