When you cant wake up for fajir and you set so many alarms and try everything to get up and pray but it still doesnt help. Dont change your volume or alarm of your phone.
But know that you need to change something you do daily in your live in order to get up for fajir.
When you know you commit a certain sin everyday again; you ask for forgiveness for it. Or you do anything else and you havent done any tawbah. Start doing it, and dont quit doing it. In every salah, every day, every week every month. Ask for His forgiveness and help so you wont do it again.
See how easy fajir will be then.
Keep one thing in mind:
Its not the sleep thats keeping you away from fajir, but your own sins are keeping you away from it. ///And thats one of the many effects of sins.