Back is the first thing I taught my dog, and what I consider the easiest. If you are working on handling, I assume the dog will do a remote sit. Send the dog straight out on a blind. After the dog has picked up the birds and is coming back, have him sit before he gets back to you. Walk up there and take the dummy from him. Back up to your original position with the dog not moving. Throw the dummy over the dogs head and back to the original pile. At this point the dog should still be sitting between you and the dummy, so raise your hand and give them a command to pick up the dummy.
I hope this helps, but it is hard to give advice because I don’t know exactly where the dog is at.