Use Volume One when in trouble (5)
I believe the answer is:
avail
'use' is the definition.
(availing is a kind of using)
'volume one when in trouble' is the wordplay.
'volume' becomes 'v'.
'one' becomes 'a'.
'when in' indicates putting letters inside.
'trouble' becomes 'ail' ('ail' can be a synonym of 'trouble').
'v'+'a'='va'
'va' going within 'ail' is 'AVAIL'.
(Other definitions for avail that I've seen before include "Be of help or advantage" , "(Of no) use or benefit" , "Serve a purpose" , "Help, benefit" , "Make use, take advantage" .)