Hi mate, firstly, welcome
A leak from the attessa line is very common, looks like you've got one.
FIrstly, you will need some auto trans fluid to refill the resoviour once you are done. And a small spanner 10mm I think and some clear tubing will help you bleed it.
Leave the cap on the resoviour in the boot (minimises the fluid you will loose). Put the car up solidly on stands. Oil tray down and rags at the ready.
Take a spanner (preferably flare nut) to that attessa line. Either 17 or 19mm, can't remember. Undo it carefully (you really don't want to strip that nut) and pull it off. Pour fluid everywhere except the oil tray.
Give the thread on the fitting a quick clean, and make sure the flare fitting is smooth without gouges or bends. Also do the best clean you can on the gearbox/xfer case end.
A tiny bit of grease on the thread, and put the fitting back on nice and smooth. Pull it down reasonably tight but nothing silly. Clean all the bloody mess down with degreaser.
Cap off the resoviour in the boot, refill it to max. Make sure the car is out of gear and start it up.
Open the bleed nipple at the rear of the transfer case until the fluid flows smoothly without bubbles. If you are unlucky it won't come through, if so there is another breather in the attessa line in a really nasty spot above the driveshafts somewhere.
Once it is bled properly, turn the car off, take it off stands, refil the resoviour if necessary, and resume hooning.