Groups turning up ignore correction by officer (6)
I believe the answer is:
octets
'groups turning' is the definition.
'octets' can be an answer for 'groups' (I've seen this before). I am not sure about the 'turning' bit.
'up ignore correction by officer' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'ignore correction' becomes 'stet' (I've seen this before).
'by' says to put letters next to each other.
'officer' becomes 'co' (Commanding Officer abbreviation).
'stet'+'co'='stetco'
'stetco' reversed gives 'OCTETS'.
Can you help me to learn more?
(Other definitions for octets that I've seen before include "Groups of eight, often singers" , "Groups of eight peformers" , "groups of eight, say singers" , "Sets of eight" .)