The renown geneticist David Reich in his recently published book from the Oxford University press titled "Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past" (page 120) says:

The most likely location of the population that first spoke an Indo-European language was south of the Caucasus Mountains, perhaps in present-day Iran or Armenia, because ancient DNA from people who lived there matches what we would expect for a source population both for the Yamnaya and for ancient Anatolians.
First does it prove people who lived in the west of Iran in the 3rd millennium BC or even earlier were an Indo-European people?