Alarm clock controlled by mobile app

Hi. I'm new in arduino and i want to make an alarm clock controlled by mobile app (using mit app inventor 2). I'm using arduino uno, a LCD,a buzzer, a button to stop the alarm, ds3231 module ,hc-05 bluetooth and some leds. Everything is connected and is working well. So i want my arduino to recive specific time from app when to start buzzing. Can someone explain me how to do that?

Every information is highly appreciated!

Is this what your are looking for : link to reddit ?

Thank you a lot. It is very useful, but I'm looking for something that has an alarm clock