When backing up, user initially neglected prompt to save (6)
I believe the answer is:
rescue
'save' is the definition.
(rescuing is a kind of saving)
'when backing up user initially neglected prompt' is the wordplay.
'when backing up' shows that the letters should be reversed in order.
'initially neglected' means to remove the first letter.
'prompt' becomes 'cue' (synonyms).
'user' with its first letter taken off is 'ser'.
'ser' written backwards gives 'res'.
'res'+'cue'='RESCUE'
'to' acts as a link.
(Other definitions for rescue that I've seen before include "Deliver from harm" , "Deliver from danger" , "Set free from harm and evil" , "Save someone from a dangerous situation" , "Help out of difficulty, save" .)