Just inspect the element if it will be inside an iframe, it will show “in iframe” in the SelectorsHub tab.

• To write the xpath/cssSelector for any element which is inside an iframe, just inspect that element and start typing.
• To verify any selector (xpath or cssSelector) inside an iframe, first inspect any element inside that iframe in which you want to verify your selector then verify your selector.
•  You can view the below mentioned video if still you are facing any issue related to it:
  https://www.youtube.com/watch?v=ccAGj0op2J8&list=PLmRg3gEG2XIYqxpHAhr8pUu8otWmPLQfO&index=1