Repeat / Repeat again
UsageRepeat already means do or say again, so again is usually redundant. It can be meaningful only where you explicitly mean one further repetition after an earlier repeat.
Repeat
Use when
You mean say or do something again.
Example
“Please repeat the instruction for the benefit of latecomers.”
Repeat again
Use when
Avoid the extra again when it merely duplicates the meaning already carried by repeat.
Example
“Replace 'repeat again' with 'repeat'.”
Quick check
repeat again, repeated again where no second repetition is meant
Usage note