However, you can smooth a problem,or difficulties over, in which over is an adverb as part of a phrasal verb = to remove a difficulty. (Note that the verb is usually separable.)
Colonel: The negotiations have stopped. The rebel chief is very angry that our men shot his brother.
President: Hmm... we need someone who can smooth things/matters over with him.
Colonel: I suggest we send Giuseppe: he ls loyal to you and grew up in the same village as the rebel chief. We should tell him that his injured men can be evacuated, that should smooth things over - he didn't like his brother, anyway.