I first was trying to use the webinar Deploying iOS apps to the App Store, but it is terribly out of date and needs to be updated.
I'm following the procedure to deploy the iOS app to my iPhone: http://developer.xojo.com/userguide/device-deployment
Under: Add Provisioning Profile to Xcode and Devices
You can now copy the Provisioning Profile file you previously downloaded to the device:
Plug in the device via USB.
Back in Xcode, select Windows ↠ Devices (or Devices and Simulators), right-click on the device and select "Show Provisioning Profiles".
I then click the + button but the only files that were downloaded are *.cer files.
I can't figure out what I'm doing wrong.