Originally Posted by
luettchau When I try to install it there is an error and when i go to Settings>> General there is not profile option so that I can trust the developer.
If you go to Settings and there is no Profiles & Device Management option it means you don't have any profiles installed. This is the only way to install apps from third parties outside of the App Store, unless you jailbreak.

A word of caution: Be very careful installing any apps outside of the App Store. I only use it for enterprise apps for work.