Telegram bot answer chatId

Good morning,
I want to experiment the integration with a telegram bot.
How do I respond to a specific chatId (of the received message) by inserting in msg.payload.content the content read from a file.
In other words, how can I merge the input message with the content read from a file, so that I can reply to a chatId without knowing what it is.
Thanks and greetings.
Lorenzo

msg.payload.chatId should contain the chatId of the incoming message.

there is no need to join/merge, after the incoming message - pass the msg through a change node to move the current payload to something else (out of the way, e.g. msg.telegramPayload) & then through a file in to read the file then move the msg parts around to form your final payload before sending it back to telegram.

Thank you very much.
It works.
Lorenzo