Top up helpers in a mess (9)
I believe the answer is:
replenish
'top up' is the definition.
(I've seen this before)
'helpers in a mess' is the wordplay.
'a mess' is an anagram indicator.
'helpers'+'in'='helpersin'
'helpersin' with letters rearranged gives 'REPLENISH'.
(Other definitions for replenish that I've seen before include "Fill up again, say glass with drink" , "Help siren (anag) - fill up again" , "Replace" , "Restock, refill" , "Help siren (anag) - make up" .)