After final word, detective reforms (6)
I believe the answer is:
amends
'reforms' is the definition.
'after final word detective' is the wordplay.
'after' is a charade indicator (letters next to each other).
'final word' becomes 'amen' (I've seen this before).
'detective' becomes 'ds' (detective sergeant).
'amen' next to 'ds' is 'AMENDS'.
(Other definitions for amends that I've seen before include "Make them to compensate" , "Make these to right wrong" , "Corrects" , "Redress" , "Improves - damages" .)