As long as you have 2 people, an Argentavis with plenty stamina, and plenty of tranq darts, this is not a problem to get. Have the better shot, shoot tranqs until it falls. I’ve found it best to fly straight at it from slightly above since tranq darts have bullet drop. This will also prove easier to see where the target is. Along with this, remember to not tranq it over any body of water, it will sink and your work will be for nothing. Keep narco berries and higher quality meats on hand for the taming process, or at least enough to hold the bird over until you can make it to your home and back with the resources necessary. Hope this helps a bit!