Assumed it's turned down (3,2)
I believe the answer is:
put on
'assumed' is the definition.
(synonyms)
'turned down' is the wordplay.
'turned' says the letters should be written backwards.
'down' becomes 'not up' (I've seen this in another clue).
'notup' written backwards gives 'PUT-ON'.
'it's' acts as a link.
(Other definitions for put on that I've seen before include "Apply (to a surface) - present (on stage)" , "Increase as with weight" , "Donned" , "Assume < present" , "Affixed" .)