He wrote about this on his page on Twitter.

“Since his American visa doesn’t allow him to get to the studio, the studio arrived on an Iranian mission in New York,” Aracci said, attaching a photograph to the post that shows Zarif giving an interview to reporters of the television program Face the Nation.

@JZarif interview with "Face the Nation".
Since his US visa doesn't allow him to go to the studio, the studio came to Iran Mission in NY. pic.twitter.com/0iSGatJ32f

- Seyed Abbas Araghchi (@araghchi) September 21, 2019

Earlier it became known that Zarif will pay a visit to New York on September 20 to attend the 74th session of the UN General Assembly.