How to receive PUSH notification when the value is < 30?

Hi, what is the working method to receive a push notification?
I have an esp8266 device that sends values ​​to firebase real time database, I would like via Kodular that when the value is less than 30 a push notification is sent (even with the app not open)
I need the notification to be sent only to the user who has the value below 30.
Thank you all.

Can anyone advise me?
Thank you.