If it's a 500 1.2 then the drain plug is on the rear trailing face of the gearbox. The filler plug is on the leading face, from memory. I can't find the handbook to tell you what type of oil you need or how much (1.3 or 1.6 ltrs rings a bell) and if you want the OE Selenia one you have to hunt around a bit for it.. but you stick in the correct amount with a +/- until the oil reaches the level of the filler hole.
The drain and filler are both 22mm allen screw/plugs.
Ralf S.