Sort out a French composer (7)
I believe the answer is:
unravel
'sort out' is the definition.
(I've seen this before)
'a french composer' is the wordplay.
'a french' becomes 'un' ('a' in French).
'composer' becomes 'ravel' (I've seen this before).
'un'+'ravel'='UNRAVEL'
(Other definitions for unravel that I've seen before include "Sort out" , "Unpick, untangle" , "Undo; begin to collapse" , "Straighten out" , "Disentangle or undo like knitted fabric" .)