Calm down — you have two presents (3,3)
I believe the answer is:
now now
'calm down' is the definition.
(I've seen this in another clue)
'two presents' is the wordplay.
'two presents' can mean two substitutions for 'present'.
'present' becomes 'now' (both can mean the current period).
'present' becomes 'now' (both can mean the current period).
'now'+'now'='NOW NOW'
'you have' acts as a link.
(Other definitions for now now that I've seen before include "It's said to reprimand or pacify a person" , "Warning" , "stop bickering" , "said to calm one down" .)