Is there a way to get user activity data (like step count, sleep details, walking distance etc) that is stored on the phone via a Facebook messenger bot?
If the bot cannot retrieve it automatically, it is okay even if there is an option for the user to share that other than manually typing it(like location sharing, which is also not available automatically).
What you've requested is currently not possible.
I'm also not sure I would want to share this information with a Facebook Messenger Bot.