How to upload to Test Flight

I am severely struggling, I am trying to figure out how to upload my IPA to test flight? I developed and Xamarin Cross Platform app on a windows box. I have previous versions from last year on Test Flight but I cannot figure out how to get the IPA back up. Something has changed since I last used test flight. I have searched and searched and I cannot find out how
How to upload to Test Flight
 
 
Q