Kivy - Confused about how to call a function from a kv element

Question

I feel that I have tried every combination of 'self', 'root' and whatnot to figure this out, and my old thick brain just can't get it.

I have a kv file that has a button nested three levels down in the tree. I have an independent function in main.py that I want to process when I press the button in the kv file.

What the heck do I write to get the button to trigger the function??? If I had any hair left it most likely be all ripped out by now.

The main.kv file (simplified):

MDBottomNavigation:
    MDBottomNavigationItem:
        text: 'Run'
        name: 'screen1'
        icon: 'yahoo'
        FloatLayout:

            Label: 
                text: 'OctopiLaser'
                pos_hint: {"x":0.3 , "y": .9}
                color: [0, 0, 0, 1]
                text_size: self.size
                font_size: 40
                bold: True

    MDBottomNavigationItem:
        text: 'Move'
        name: 'screen2'
        icon: 'yahoo'
        FloatLayout:
            height: .7
            Button:
                background_normal: 'images/arrowUp.png'
                background_down: 'images/arrowUpDn.png'
                size_hint: (None, None) 
                pos_hint: {"x":0.04 , "y": .43}                
                on_press: moveCommand('jog','z', root.dist * 1)
                                ^
                                |
                                | I want to get this function to execute

The section of main.py that I am trying to reference:

class TimeLabel(Label):
    def __init__(self, **kwargs):
        super(TimeLabel, self).__init__(**kwargs)
        self.text= str(time.asctime())
        Clock.schedule_interval(self.update,1)

    def update(self, *args):
        self.text = str(time.asctime())
        print (self.text)

#*****************************************************************
class moveWindow():
    def getinfo():
        pass
    def moveCommand(self, motion, axis, quantity):
        print (motion)
        print (axis)
        print (quantity)
        if motion == 'home':
                blah blah blah

I know that the answer is probably simple, but it eludes my mind. Please help!