Pwntoy

I was trying to teach my nidorino TM28, Dig, in Mt.Moon but when the game prompted me to choose a pokemon to learn dig, I tapped Nidorino and nothing happened. I restarted the game after the same thing happened three more times and when I looked at my TM tab, Dig was gone. Is there another way I can get a second TM 28? I just beat Misty and I need to rely on it for the 3rd gym.