This may be what you want to do with the ability of the device to automatically rotate the screen when the device is turned 90 degrees.
Presently, the default ScreenOrientation setting is set to Unspecified. This permits the screen to rotate automatically in an App Inventor 2 App.

You can force the App to stay in Portrait or Landscape mode by selecting the appropriate choice.
Is that what you wanted to know?
Regards,
Steve