Or is there a dua that I can say and ask Allah to let him know? Is it okay to play the azaan if it is not prayer time?
1) There is a saying in Arabic- The real value of a bounty is appreciated only after it disappears. Allah has bestowed us with parents. There real value dawns on us only after they leave this world. Nevertheless, Allah is Most Merciful. He affords us opportunities to make up for our shortcomings. It is mentioned in a hadith that if a child makes dua for his deceased parents, he is regarded as obedient. We advise you be obedient to Allah and make dua for your father. Also perform good deeds for example, give charity etc, with the intention of giving the reward to your father. Your father is more in need of you now than he was in his lifetime. He will receive the rewards you send for him and will appreciate that.
2) It is permissible to play the azaan out of salat time.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai