Currently, Fitbit does not share data in order for our developers to integrate it into Lark, but we are currently working to add a feature that allows users to add steps soon.
In the meantime, you can always manually add activity in Lark. One way to do so is by tapping on the plus symbol at the bottom and then tapping “Add data”. You can also add activity by tapping on the profile icon at the upper left side (or upper right side in Android) and then go to the activity tab. You will then see a plus symbol you can tap on to log your activity.