Helping to release one in desert (3,2)
I believe the answer is:
rat on
'desert' is the definition.
(I've seen this before)
'helping to release one' is the wordplay.
'helping' becomes 'ration' (a ration is a serving or helping).
'to release' indicates named letters should be taken away (letters are released or freed).
'one' becomes 'i' (Roman numeral).
'ration' with 'i' taken away is 'RAT ON'.
'in' acts as a link.
(Other definitions for rat on that I've seen before include "shop" , "Betray" , "desert" , "grass up" , "Give away" .)