smooth down
To cause something to lie and remain flat and smooth with or as with one's hand or hands. A noun or pronoun can be used between "smooth" and "down." I've been trying to smooth down my hair ever since I woke up, but this bed-head is just too stubborn! I got up off the bed after my nap and smoothed the sheets down.
smooth something down
to make something flat or smooth by pressing. she smoothed her skirt down, fluffed her hair, and went into the boardroom. Karen smoothed down the bedclothes.