Due to Apple’s policy, an "Untrusted Enterprise Developer" prompt appears when you first install an Enterprise app on iOS.
The solution is as follows (take iOS11 system as an example)：
1、Open the settings function in your phone and select "General"
2、In General, select the "Profile and Device Management" feature.
3、In the enterprise application classification in the description file and device management, select the file name of the enterprise application to be installed (consistent with the prompt when opening), click to enter
4、After entering the company signature page, after confirming the company name and application name in the company signature, click Trust "Enterprise Signature Company Name"
5, back to the desktop, re-open the application to use