Вот первый хендлэр:
@dp.message_handler(commands=['start'])
async def start_menu(message: types.Message):
    global paste_username, paste, username, math_equation_result
    await Mydialog.captcha1.set()
    CAPCTHA_SIZE_NUM = 2
    generator = CaptchaGenerator(CAPCTHA_SIZE_NUM)
    captcha = generator.gen_captcha_image(difficult_level=3)
    math_captcha = generator.gen_math_captcha_image(difficult_level=2)
    image = captcha.image
    characters = captcha.characters
    math_image = math_captcha.image
    math_equation_string = math_captcha.equation_str
    math_equation_result = math_captcha.equation_result
    
    image.save("captcha.png", "png")
    math_image.save("captcha.png", "png")
    photo = open("captcha.png", "rb")
    await bot.send_photo(chat_id=message.from_user.id, photo=photo)
    await message.answer('Чтобы начать работу, решите математический пример!')
    print(math_image)
    print(math_equation_string)
    print(math_equation_result)
    username = message.from_user.username
Второй хэндлэр (после elif '/start' in message.text нужно вызвать выполнения функции start_menu с первого хендлэра):
@dp.message_handler(state=Mydialog.confirm)
async def agree(message: types.Message):
    try:
        if '⛔️ Отмена' in message.text:
            await message.answer('Всего хорошего!', reply_markup = ReplyKeyboardRemove())
        elif '✅ Согласен' in message.text:
            await message.answer('Чтобы продолжить, подпишись на наш Telegram : \n@test_prize \n<link>', reply_markup=telegram_buttons)
            await Mydialog.telegram.set()
        elif '/start' in message.text:
              start_menu()
    except:
        pass