Kivy: action when unclick a checkbox

I am creating a mobile app as questionary, my questions are in checkboxes. functions in my app make a list of answers and when the user choose certain answer it writes value into list.

Sometimes they can choose wrong answer and they want to repair their choice. i want to add function when they unclick a checkbox to delete last value in list

in .py

class test:

    def __init__(self, testovatel, test_v=[], ):
        self.testovatel = testovatel
        self.test_v = test_v

    def mistake(self):
        del self.test_v [len(self.test_v)-1]


class TestScreenV(Screen):
    
    jarka= test("jarka")

    def bad(self):
        if self.ids.check_test.active == False:
            self.jarka.mistake()

    def d_plus(self):
        self.jarka.test_v += ("d",)

    def i_plus(self):
        self.jarka.test_v += ('i',)

    def s_plus(self):
        self.jarka.test_v +=('s',)

    def k_plus(self):
        self.jarka.test_v +=('k',)

in .kv

<TestConfirm>
    on_release: root.set_icon(check_test)
    CheckboxLeftWidget:
        id: check_test 
<TestScreenV>:
    OneLineListItem:
        text: "1/24 "
                            
    TestConfirm:
        text: "bla"
        on_press: 
            root.d_plus()
            root.bad()
    TestConfirm:
        text: "bla"
        on_press: 
            root.k_plus()
            root.bad()
    TestConfirm:
        text: "bla"
        on_press: 
            root.s_plus()
            root.bad()
    TestConfirm:
        text: "bla"
        on_press: 
            root.i_plus()
            root.bad()