In order to install your test app on an iOS device prior to submitting it to the Apple App Store, you must first define that device as a test device in the iOS Dev Center.
1. To login into the iOS Developer Console go to <https://developer.apple.com> and click Account at the top
Finding the device UDID
In iTunes, you can find it when your iOS Device is connected to the computer.
Steps to Find UDID-
- Connect your phone to your Mac with Catalina
- Launch Finder
- Click on your phone in Finder under Locations in the side bar (if you don't see the side bar on the left click on the View menu/Show Sidebar)
- On the Summary screen that appears click on the line below the phone's name (click on the phone model)
- View the serial number, UDID and model code
Adding new device into apple dev center.
-By entering Platform, Device Name and the UDID and then click on save.
Now Device has been added into Apple dev account.
Adding a new device to the Ad Hoc Profile
1. Go to the iOS Provisioning Portal and click on Provisioning. Select the Distribution tab.
4. In the bottom select the new devices you want to add to your Ad Hoc profile and click on save and Generate a new one by downloading.
Once you have completed this step for ALL of the devices you want to test with, you can create your Ad Hoc Provisioning Profile by following this article - iOS - Creating an Ad Hoc Distribution Provisioning Profile