Relax and open the car window (4,4)
I believe the answer is:
wind down
'relax' is the definition.
(to wind down is to relax or chill out)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for wind down that I've seen before include "Relax after stress" , "Chill" , "Relax after activity" .)