I train mine and any new ones to come in by pairing honking a horn with getting some grain. Some of our pastures are a few thousand acres.
Honk the horn, go look for them. Honk when I see them. Get closer. Honk when close enough for them to see/hear grain in bucket. They come close. Honk right before doling out the treats. Only takes 3 or 4 times before they come running in when they hear the horn. Most here have a smaller overnight pen, some corrals, or a small couple acre paddock we catch into.
Silly me, I used to try to whistle or yell to them. A neighbor used his truck horn, too. Until it quit. Then he bought an old trumpet at a pawn shop and sqwaks loudly on it. He's hilarious. It works with his cows, too.
If you have neighbors close by, maybe you should warn them if you try this. :)