What kind of context would this be used in?
A: What did you say?
B: Fine, I'll repeat.
I repeat. What do you want?
I repeat. Your number is..., correct?
I've always heard it in context of speech, as in asking someone to repeat something, so I'm blanking on whether it can be used elsewhere.
So if I say "bạn lặp lại làm ơn", will people understand I want them to repeat what they said? :D
That would be a very weird sentence to say. You may say these instead:
Làm ơn lặp lại (giúp tôi)! -> Please repeat that (for me)!
Bạn có thể lặp lại (giúp tôi) được không? [More polite] -> Could/Can you please repeat that (for me)? Would you mind repeating that (for me)?
I would just say 'nói lại' - 'Say again'