You may use up to two “fè” in that sentence; the third one will indeed make it confusing.
Kouman w fè l?
How do you do it?
Kouman ou fè fè l?
How did you succeed in doing it?
Do you think they were trying to say something other than what I have above?
Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words