So, if I wanted to reset an alarm that was in progress, for a school project, I'd wire in a button and code that when the button is pressed, stop the wailing and gnashing of teeth. But you know that already cause you did an internet search on the words "arduino alarm", right? After all, it makes sense that many people have done Arduino Alarms for as long as the Arduino has been in existence, there would be example codes on the Internet, right?
Post the code that you have so far and a wild guessing how stopping the alarm might work
best regards Stefan