Prepare to Make Unreal Games with Unreal Engine – Installing and Setting Up - Learning Unreal Engine iOS Game Development - page 10

After building, the Unreal Editor will run automatically. Whenever you want to run the
Editor, you don't have to build it again; you just need to browse to the build location and
open it. The location for Mac and Windows is as follows:
For Mac: UnrealEngine-4.3.0-release /Engine/Binaries/Mac/
UE4Editor-4.3.0.app
For Windows: UnrealEngine-4.3.0-release /Engine/Binaries/Win64/
UE4Editor.exe
Keep in mind that the final *.app name might be different; it depends on the build type
you made. Here, I made a debug engine build and my final engine application file was
named Debug.app by default, which I then changed to UE4Editor-4.3.0 . Feel free
to change it; as long as you have different engine builds running at the same time, you will
need to define them to avoid any confusion.