Hi Buddy,
There's a simpler solution, where you retain control.
Run the app on your Mac, in the Simulator, and take the screenshots from the Simulator.
From Xcode, Build/Run on iOS Simulator - iPad Pro (12.9 inch)
From the Simulator, "File" menu, "Save Screen Shot"
Note that the resolution of the screenshot depends on the zoom level that the Simulator is using - e.g. "Window", "Scale", "100%" (it doesn't matter if it's too big to fit on screen).
No worries,
- Rob.