How can i set ringback music

Ringback tones, which are heard by the person calling you, rather than by you, are not something you can set up on the device. It isn't part of the phone and there are no apps for it. Unless you are using an app that calls that app rather than your phone directly.

They are through the carrier/service provider only. So first you would need to see if your carrier/service provider even offers them. Then, if they do, it will probably be an additional fee to have them on the account. Once you do all that, then you can set it up to play what you want, from the music that your carrier/service provider allows.