I tried Telegram at first and found several channels all claiming to be official, but without obvious instructions for such a bot. Then I tried Googling, and there are countless shady links. It's unclear what the real thing is and what's a scam/spam.
Tap the share button to email the book to your Kindle email address.
If the Kindle has wifi on, the book automatically appears under another 10 seconds.
The whole process takes less than 30 seconds.
I buy Kindles specifically for this feature of being able to mail EPUBs to Kindle. When or if it is no longer possible, I stop buying Kindles.