1. Go to Hearthome City and enter the Pokemon Fan Club, which is located in the southwest of the city center.
2. Inside the Pokemon Fan Club, find a man standing near the entrance. He will challange you to a Pokemon battle.
3. After you defeat him, he will offer you a reward, which is a random TM. The TM peck has a 5% chance of being the random reward, so you may have to battle him several times to obtain it.