Others may have a better way to repair pulls in berber carpet, but here is what I did. Get yourself some crazy glue and some straight pins. Separate the pile so you can see the spot that the loop pulled away from. Place a small drop of glue on the spot. Use a pin to place the matching part of the loop in place and secure it until the glue dries. After it's dried, carefully remove the pin. This works well for small pulls, up to a couple of loops. Any more than that and it can get messy.