Blokes in commercial meant to forget a correction (9)
I believe the answer is:
amendment
'correction' is the definition.
(amendment is a kind of correction)
'blokes in commercial meant to forget a' is the wordplay.
'blokes' becomes 'men' (bloke can informally mean a man).
'in' means one lot of letters goes inside another.
'commercial' becomes 'ad' (abbreviation for advertisement).
'to forget' indicates named letters should be taken away.
'meant' with 'a' taken away is 'ment'.
'men' put inside 'ad' is 'amend'.
'amend'+'ment'='AMENDMENT'
(Other definitions for amendment that I've seen before include "the fifth one benefiting Uncle Sam's defendants?" , "maybe fifth taken by US criminal" , "A qualification" , "change for the better" , "Addition or alteration, to a motion or official document, say" .)