Answer
Verse 109 / 110 Surah 18 ? Surah Kahf should be recited before sleeping intending in your mind what time you wish to wake up, having full trust on Allah. It has been the experience of our pious predecessors that this was very effective in awakening a person who read it at the actual time desired.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai