Once you download the app, click it to open and if you see the 'Untrusted Enterprise Developer' alert. Please follow below steps on your device and then try to open app again.

• In iOS 10+, go to Settings - General - Device Management - tap on your Profile - tap on Trust button.
• In iOS 9.2+, go to Settings - General - Profiles & Device Management - tap on your Profile - tap on Trust button.
• In iOS 9.1 and lower, go to Settings - General - Profiles - tap on your Profile - tap on Trust button.