What should someone do who prepares all the means to wake up for the fajr prayer but still doesn't wake up?

He should keep making du'a, ask someone to wake him up, arrange a fajr program like reading Quran with a group, or walking with a group, for example, they say every day we walk.

This gives some motivation to wake up so I can go walk with them. This is at the beginning until he gets used to it.

To waking up, inshaAllah. Let people invite each other for breakfast every day, inshaAllah.

So, inshaAllah, he will get up.