Delete because entered before (5)
I believe the answer is:
erase
'delete' is the definition.
(erasing is a kind of deleting)
'because entered before' is the wordplay.
'because' becomes 'as' (I've seen this in other clues).
'entered' is an insertion indicator.
'before' becomes 'ere' (usually literary**).
'as' placed into 'ere' is 'ERASE'.
(Other definitions for erase that I've seen before include "Scratch" , "Remove from memory" , "To remove all trace" , "Remove evidence of" , "score" .)