I've read on the difficulties (and workarounds) for "racing an activity" when I've got it on the watch.
And I can't believe you can't simply select an old activity from history on the mobile app and hit "send to device". However...
On the website you can do "send to device". But it doesn't seem to do anything. Is that because I'm assuming it will happen wirelessly (similarly to the way apps are installed)? Do I need to physically connect the watch to my PC to transfer like this? And if so, do I need to install the Express app too?