Dolly Parton's behind first benefit (6)
I believe the answer is:
assist
'benefit' is the definition.
(I've seen this before)
'dolly parton's behind first' is the wordplay.
I cannot really see how this works, but
'behind' could be 'ass' (both can mean one's back side) and 'ass' is found within the answer.
'first' could be 'ist' (ist resembles 1st) and 'ist' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for assist that I've seen before include "Work as a subordinate" , "Work with N help" , "Expedite" , "Help to make" , "provide backing" .)