1
Choose a revealing excerpt
Pick a sentence followed by a pause. The pause makes lingering room sound easier to hear; include a few quiet consonants so you can check whether speech survives.
2
Try a conservative pass
Open an audio cleaner or editing tool that offers suitable voice processing. If it provides an intensity control, begin gently rather than assuming the strongest setting will sound best.
3
Match levels and compare
Listen to the original and processed excerpts at similar volume. Check the ends of words, pauses, and changes in vocal tone before applying the same approach to the full file.