Cleaner more confident about officer (7)
I believe the answer is:
scourer
'cleaner' is the definition.
(I know that scourer is a type of cleaner)
'more confident about officer' is the wordplay.
'more confident' becomes 'surer' ('sure' can be similar in meaning to 'confident').
'about' is an insertion indicator.
'officer' becomes 'co' (Commanding Officer abbreviation).
'surer' going around 'co' is 'SCOURER'.
(Other definitions for scourer that I've seen before include "one employed to wash pots?" , "One searching" , "A cathartic" , "Pan cleaner" , "Abrasive cleaner" .)