I have created an application. In that, I have to list of audio files and "Set as ringtone" option there. I don't know how to set audio file as ringtone.
You cannot. Apple doesn't release an API to export/write ringtones to the operating system. But u can make ur audio as ringtone through itunes
Use iTunes file sharing in your app and copy the ringtone file to the app's documents directory.
Set "Application supports iTunes file sharing" to YES in your info.plist