Set up nicely to hold back contribution (5)
I believe the answer is:
input
'contribution' is the definition.
(input means someone's contribution to something)
'set up nicely to hold back' is the wordplay.
'to hold' indicates a hidden word (I've seen 'holds' mean this).
'back' is a reversal indicator.
'tupni' is hidden in the letters of 'set up nicely'.
'tupni' backwards is 'INPUT'.
(Other definitions for input that I've seen before include "Insertion of data" , "Data supplied to computer system" , "Signal feeding a circuit" , "supply" , "Contributory remark(s)" .)