Repeating something from the start

फिर से

English Usage: I will try that task over again.

Hindi Usage: मैं उस कार्य को फिर से कोशिश करूँगा।

Doing something one more time

एक बार फिर

English Usage: Please say it over again, I didn't hear you.

Hindi Usage: कृपया इसे एक बार फिर कहें, मैंने आपको नहीं सुना।