This is common with Rottweiler puppies, and owners planning on showing or who just worry about the look of the adult dog, don't wait and see. For mild cases, they massage the ear crease to try to return the ear to the desired fold. For cases that don't respond to that, they tape the ears into the proper position until teething is over to train it into the proper fold. It happens most often with puppies who have thin ear flaps - or short ones. I only had to do it with one of mine, but I'm glad I did.
If you Google around about taping puppy ears, you'll find several methods. I used the one where there's tape down each side of each ear, and it meets under the jaw. It needed redoing regularly, but wasn't hard. The tape to use is the inexpensive plastic stuff - I always thought of it as electrical tape. I guess some puppies are difficult because they rub it off, but mine wasn't bothered. In her case, she has lightweight ear flaps, and one still as a adult turns upside down regularly, but they hang properly.
