Python: break a timer.repeat() after time went zero (on raspberry pi)

i am programming a pythonscript with guizero. there is a PushButton and its command runs a function. This function ist build after a PomodoraTimer Tutorial i found on youtube. As far, it works, but i want it to stop, after the alarm is running. The Code is the following:

#UserInterface, GPIO-Steuerung und Timer-Steuerung importieren
from guizero import App, Text, TextBox, PushButton, Box, Window
import RPi.GPIO as GPIO
import time
import datetime

#this is what gets triggered by the Pushbutton
def startTimer():
    global timer
    if (set_time_input.value == "" and set_time_input_min.value == ""):
        currentTimeLeft = "3" #60 #set timer to 1 minuit if textfield empty
    else:
        if (set_time_input.value != ""  and set_time_input_min.value == ""):
            currentTimeLeft = int(set_time_input.value)
        else:
            currentTimeLeft = int(set_time_input_min.value) * 60

    #Countdownanzeige
    timer = Text(timer_box, text="\r"+str(currentTimeLeft), size=30, color="red")
    timerbottom = Text(timer_box, text="\n Sekunden.")
    timer.repeat(1000, reduceTime)

def reduceTime():
    global timer
    if int(timer.value) > 0:
        timer.value = int(timer.value) -1
    else:
        start_alarm_1() #this triggers a GPIO on my Raspi for 3 seconds
        #exit()

#####this is just the rest of the app if ou want to build it and test it:

#GPIO Steuerung initialisieren
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.cleanup()

#Start Alarm -> i've got a remote alarm that works this way ;)
def start_alarm_1():
    GPIO.setup(20, GPIO.OUT)
    GPIO.output(20, GPIO.LOW)
    time.sleep(3)
    GPIO.output(20, GPIO.HIGH)
#App-Fenster initialisieren
app = App(title="OSCE Timer", width=800, height=400)
#textfields to set timer time
textfield_msg = Text(app, text="Timer in seconds:")
set_time_input = TextBox(app)
textfield_msg = Text(app, text="OR timer in Minutes:")
set_time_input_min = TextBox(app)
run_timer_button = PushButton(app, command=startTimer, text="start Countdown")
#timer window in app
timerTitle = Text(app, text="Time:\n")
#Appwindow
app.display()

My problem is: if in the reduceTime() the timer.value gets "0", then the alarm starts over and over again. this is because the timer.repeat() function is triggering the reduceTime() function over and over again - for ever. Now i had multiple ideas: build a while-loop around the repeat() function, add return -1 statements to different places, but none of it worked. I would be so happy if anyone could help me! (the problem with the while statment: it doesnt display my timer anymore because the function is stucked in the while loop obv.)

Damn, after hours of trying i posted this - and few seconds later I found a solution!

I had to add the following line insted of the '#exit()' statement i also worked with:

time.cancel(reduceTime)