There is no way to use iHeartRadio application on your Nintendo 3D XL because the device does not have Flash support which is a requirement.
If you want to add music on your device, please install iTunes and add the music to a playlist, right click on the tracks of your choosing and select Create AAC version. Plug in the SD card of Nintendo device to a computer then drag the AAC tracks from iTunes to the root of the SD card. Plug the SD card back to Nintendo and select the music application.
