The steps to set the incoming call ringtone on Duoduo Ringtone are as follows:

1. Open the phone settings interface and find the "Sound and Vibration" option.

2. Click the "Incoming call ringtone" option and select Duoduo ringtone in the ringtone list.

3. Click "OK" to save the settings, and the Duoduo ringtone will become the incoming call ringtone. Duoduo Ringtone is a mobile ringtone application that provides a large number of ringtone resources, including popular songs, classic old songs, movie soundtracks, animation music and other types.