I have deleted an activity on Garmin Connect by mistake and I would like to get it back. Whenever I sync my Edge 810, the activity does not show up anymore. How can I make Garmin Express re sync?
This all depends on whether the Activity is still present in the History menu on the Edge 810. If you can still pull the activity up in the History menu then you can use the manual upload method to get it back in Connect. If the activity has been deleted from the Edge 810 it will no longer be available.
Once you have confirmed the activity is in the History menu on the Edge use the FAQ: How do I manually upload data from USB Mass Storage devices to Garmin Connect? to upload it to Connect.