To build your project using IL2CPP, open the Build Settings window (File > Build Settings). Select the platform you are building for, then click Player Settings to open the Player settings in the Inspector.
In the Project Settings window, locate the Player settings for your target platform, and scroll down to the Configuration section. For Scripting Backend, select IL2CPP.
With IL2CPP selected as the Scripting back end, click Build in the Build Settings window. Unity begins the process of converting your C# code and assemblies into C++ before producing a binary file for your target platform.