Answer:
I'd travel back to when I was in elementary school, when I was still being bullied.
Step-by-step explanation:
Back then, I didn't exactly know how to defend myself and I always relied on others (which I still kind of do now but now I do more things myself). If I was able to go back there, I'd meet my past self and I would help them with the bullying problem, and help them learn to defend themselves.