Yankee repairman quietly turning over deck (8)
I believe the answer is:
prettify
'deck' is the definition.
(thesaurus)
'yankee repairman quietly turning' is the wordplay.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'repairman' becomes 'fitter' (worker who fits something).
'quietly' becomes 'p' (p for piano and quiet).
'turning' is a reversal indicator.
'y'+'fitter'+'p'='yfitterp'
'yfitterp' backwards is 'PRETTIFY'.
'over' is the link.
(Other definitions for prettify that I've seen before include "Doll up" , "Make superficially attractive" , "tart up" , "Ornament" .)