Pen-pusher said to be one who corrects what’s wrong (7)
I believe the answer is:
righter
'be one who corrects what's wrong' is the definition.
'pen-pusher said' is the wordplay.
'pen-pusher' becomes 'writer'.
'said' shows a homophone (sound like).
'writer' sounds like 'RIGHTER'.
'to' is the link.
(Other definitions for righter that I've seen before include "One who rectifies" , "Person making corrections" , "He sets all straight" .)