Speaking to the House Foreign Affairs Committee yesterday, Secretary of State Rex Tillerson was asked about whether or not the Trump Administration's policy is one of trying to impose regime change on Iran. While Tillerson insisted that the specifics of administration policy on Iran are still under development, he did confirm that the goal remains regime change.
Exactly how they expect to pull that off remains to be seen, but Tillerson said the US policy as it stands is to rely on "elements inside of Iran" who can be supported toward the end goal of regime change, with the hope it would be a "peaceful transition of that government."
That's unlikely, as to the extent US officials have shown interest in supporting "elements" in Iran at all, it's groups with long-standing links to terrorism like the Mujahedin-e Khalq (MeK). The actual reformists within Iran's political system tend to be vilified by the US, and even when they do take power, as they have now, US hostility tends to undermine their ability to normalize ties with the West.