pyTelegramBotAPI/examples/asynchronous_telebot/chat_join_request.py

from telebot.async_telebot import AsyncTeleBot

import telebot
bot = AsyncTeleBot('TOKEN')

@bot.chat_join_request_handler()
async def make_some(message: telebot.types.ChatJoinRequest):
    await bot.send_message(message.chat.id, 'I accepted a new user!')
    await bot.approve_chat_join_request(message.chat.id, message.from_user.id)

bot.polling(skip_pending=True)