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' is a deletion indicator (letters are released or freed).
'one' becomes 'i' (Roman numeral).
'ration' with 'i' removed 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" .)