Heroic exploit about start of victory is made up (7)
I believe the answer is:
devised
'made up' is the definition.
('devise' can be a synonym of 'make up')
'heroic exploit about start of victory is' is the wordplay.
'heroic exploit' becomes 'deed' (I've seen this before).
'about' means one lot of letters goes inside another.
'start of' indicates taking the first letters.
The initial letter of 'victory' is 'v'.
'v'+'is'='vis'
'deed' placed around 'vis' is 'DEVISED'.
(Other definitions for devised that I've seen before include "Invented" , "Conceived" , "Came up with, a plan say" .)