How to identify a modal iOS window via appium?

Hi all,
I am having an issue while automating iOS app via appium. The problem I am facing is our app has modal window comes up on clicking some link in app, and I need to tap on some element inside that modal window. But I haven’t been successful.

Basically, my suspicion is previous window before modal window is blocking to interact with modal window. If some one can suggest on how to switch to interact with that modal window, it would be really helpful.