Pressed De Niro by mistake (6)
I believe the answer is:
ironed
'pressed' is the definition.
(ironing is a kind of pressing)
'de niro by mistake' is the wordplay.
'by mistake' indicates anagramming the letters.
'de'+'niro'='deniro'
'deniro' is an anagram of 'IRONED'.
(Other definitions for ironed that I've seen before include "De Niro (anag)" , "flattened" , "prepared for 23 [WARDROBE] ?" , "Made smooth, shirt or collar" , "Smoothed the cloth with heat" .)