Repeat the crimson zero (4)
I believe the answer is:
redo
'repeat' is the definition.
(I've seen this before)
'crimson zero' is the wordplay.
'crimson' becomes 'red' (synonyms).
'zero' becomes 'O' (O resembles 0).
'red'+'o'='REDO'
'the' acts as a link.
(Other definitions for redo that I've seen before include "Have second thoughts" , "Start again" , "further attempt?" , "Redecorate or repeat action" , "Decorate (eg a room) again" .)