Check to see if the device shows up.
NOTE: In the event of a partially complete enrollment, you may see the device in the administrator portal. It may also have some incorrect information such as showing noncompliant, showing wrong version, etc)
Remove the device from within the administrator portal.
NOTE: There is not an application installed on iOS devices, just the management profile.
Remove the management profile on the iOS device. Navigate to Settings > General > Profile & Device Management, tap on the app's configuration profile.
Then tap Delete Profile. If asked, enter your device passcode, then tap Delete.
NOTE: Some iOS devices may vary for where the management profile needs to be deleted. For this information, please consult Apple.