but, @Maria, i know that time is short and you have deadlines, but i still ask what i asked several days ago:
are you positive that you have a reliable working internet connection between board - blynk server?
you should test it first, with a sketch containing nothing else just to send uptime to app. if you can not make that working, it is not reasonable to struggle with more advanced things.
in the sketch builder you can find example for that.
i have a feeling that you're acting in haste, but you should slow down, and go in very small steps. as i already wrote:
1) the flame sensor sketch is working as you wish in offline mode (without internet and blynk)? just with a buzzer. yes / no ?
2) do you managed to have a working sketch with serial usb or whatever connection to blynk? just sending uptime for some minutes. (no notification or flame sensor involved) yes / no ?
3) ONLY if 1 and 2 are positive it worths trying to implement flame sensor and notification to the sketch.