At heart, many need to help out (4)
I believe the answer is:
amid
'at heart many need' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'to help out' is the wordplay.
'to' becomes 'm' (I can't justify this - if you can you should believe this answer much more).
'help' becomes 'aid' ('aid' can be a synonym of 'help').
'out' means one lot of letters goes inside another.
'm' inserted into 'aid' is 'AMID'.
Can you help me to learn more?
(Other definitions for amid that I've seen before include "A dim sort of preposition" , "Among" , "In the course of" , "Surrounded by" , "In the thick of" .)