Cannot Find a Windows Open File window's "File name" TextBox

Hi,
I am a relative newbie, so I apologize if this has already been asked and answered.
I am writing tests for a Windows 10 application with Appium WinAppDriver in c#
I am having issues with SendKeys to enter a string in a Windows Open File window’s “File name” TextBox.
Appium does not seem to be able to Find the window or TextBox.What “AutomationId” should I be using? Any ideas?

Thank you in advance.