As before, about to obliterate (5)
I believe the answer is:
erase
'to obliterate' is the definition.
(I've seen this in another clue)
'as before about' is the wordplay.
'before' becomes 'ere' (poetic term for 'before').
'about' is an insertion indicator.
'as' inserted inside 'ere' is 'ERASE'.
(Other definitions for erase that I've seen before include "Clear" , "Take out" , "To remove all trace" , "score" , "Destroy recording on audio or video tape" .)