It can cure cold feet if nerve goes after trouble (3-5,6)
I believe the answer is:
hot-water bottle
'it can cure cold feet' is the definition.
The definition suggests a singular noun which matches the answer.
'nerve goes after trouble' is the wordplay.
'nerve' becomes 'bottle' (I've seen this before).
'goes after' is a charade indicator (letters next to each other).
'trouble' becomes 'hot water' (to get in hot water is to get in trouble).
'bottle' after 'hotwater' is 'HOT-WATER BOTTLE'.
'if' is the link.
Can you help me to learn more?
(Other definitions for hot-water bottle that I've seen before include "night heater" , "comfort in retirement!" , "Bed warmer" .)