Quite simple but fiddly, have a look underneath the car and you'll see the gearbox drain plug on the box, now the fun bit, if you open the bonnet and look down in between the intercooler on the o/s of the car sat in the depths next to the turbo will be a dipstick with a ring pull, that doubles up as the fill up tube ! So pull that crack off the drain plug then refill using a big funnel and pop the dipstick back in.
I wouldn't advise doing it when hot as you will probably burn your arms a bit
Sent from my SM-G850F using Tapatalk