How to automate OAuth login screen for an iOS Native app?

Unable to spy the objects in OAuth login screen of an iOS native app installed in iPhone device. OAuth login screen contains the objects like Username text box, Password text box and Login button.

The object Spy properties dialog box opened and showed as Native-Non instrumented in the header. I am using Appium Studio tool (version 20.4.6801).

Behavior of the OAuth login screen in this application:-
Once launched this application and entered the credentials, the end point of this OAuth will hit the safari browser. Once the authentication succeed, it will be re-direct to native app home screen.

Kindly help me how to spy the object from the OAuth login screen.