I've trained all three of my labs to find antlers and have trained 2 other dogs as well.
It's actually pretty easy. First you get the dog interested in chasing and holding the antler. It's much easier with a retriever breed but you can teach the collie, they are super smart. You will need a few antlers to accomplish this task.
After they are interested I place them on the bare ground and just walk around the yard telling the dog to "find the antlers". When they come upon it and pick it up...I make a huge deal about it...telling the dog how good they are and getting really excited.
From there you put the antler in longer grass and work them on the downwind side so they can smell it.
From there you can find even longer grass, put it under leaves, cover it slightly with dirt....get creative here you know your area moreso that I do. If you are going to look on the edges of cornfields for instance, make sure you put the antler under some corn stalks. You get the idea.
Here's the most important thing I've found. I always handle the antlers with rubber gloves on. That keeps the human scent off the antlers. I also will wipe them down with paper towels when I am done and even spray scent killer on the antler itself. It doesn't kill the antler scent so don't worry.
Good luck. Have fun. The more fun you make it for your dog, the better.