Here is a summary how to upload scenarios to the Steam Workshop.
For new scenarios, just put all the files in one folder (.sce file, and any graphical assets you might have), for example
Documents\My Games\The Operational Art of War IV\Scenarios\Custom\New Scenario\.
To modify an older scenario of yours to upload it to Steam, it’s a little more complicated, because you have to gather the files into one folder. For an existing scenario like Kasserine 43, you’ll have to copy or move the needed files from the Install/Scenario and Install/Graphics to a new folder called something like Documents\My Games\The Operational Art of War IV\Scenarios\Custom\Kasserine 43.
Custom is just an example, you should use whatever folder is most appropriate like TUTORIAL.
Once you have everything in the same directory, test your scenario, then open it in the editor and select ‘Export to Steam.’ Wait about 10 seconds before closing the editor.
For updating your scenario in the Workshop, make sure you have subscribed to it yourself before doing so, to avoid creating a duplicate instead of updating the existing Workshop entry.