I cannot get_dialogs with Telethon Bot since the method is only available for a client. Therefore when I try to access the entity with its id I receive an error. How do I access an entity(channel) if I cannot parse all channels and neither access them by id? I would like to parse messages from a private group and use Telegram Bot for it.
Adding the bot to the channel while it's running should be enough for the bot to obtain its access hash. Alternatively, sending a message there while the bot is inside should also work. This hash will be saved to the .session file. Regardless, if you use the "marked" ID (for channels, prefix -100 to the real ID or use types.PeerChannel(real id)), Telethon will know you mean a channel, which can help make it work.
How to get entity of a channel using Telethon bot API?