How can I call this back-end function to the front-end

def update_rec():
    con = sqlite3.connect("customerRecord.db")
    cur = con.cursor()
    cur.execute('SELECT * FROM customerRecord')
    cur.execute('UPDATE customerRecord SET TotalPurchase = (?) WHERE TotalPurchase = (?) ')
    con.commit()

def update():
    customerDatabase_BackEnd.update_rec()