Changing settings on iPad Pro selfie camera? (2018 11 inch model)
To adjust the refresh rate and resolution of the selfie camera, you also have to adjust the video recording options of the main shooter too. Apple does not let you change the settings independently of one another. 

Go to: Settings>Camera>Record Video> “1080p at 60FPS” or “1080p at 30FPS”.

You should see the results immediately in the viewfinder.