Iran is on the tariffs list because of Trump's maximum pressure policy (an official National Security Memorandum) against Iran. This is coupled with Trump's willingness to get Russia to cooperate in the ceasefire.

I'm not claiming his administration's logic is 100% sound, only that there is an explanation that doesn't assume the rather farfetched theory that Trump is an agent for Russia.

I'm not particularly well-versed in this area, but searching for the topic on Google easily found this information on sites such as Wikipedia, WSJ, Newsweek, and whitehouse.gov.