Editor, supporting immensely, made amends (6)
I believe the answer is:
atoned
'made amends' is the definition.
(I've seen this in another clue)
'editor supporting immensely' is the wordplay.
'editor' becomes 'ed' (abbreviation).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'immensely' becomes 'aton' (I've seen this in another clue).
'ed' put after 'aton' is 'ATONED'.
(Other definitions for atoned that I've seen before include "Made up for past wrongdoing" , "Made up for past offence" , "Made reparation (for)" , "Expiated" , "Made amends" .)