its pretty easy, first edit the scenario IN GAME (WHILE PLAYING IT, USING GOD MODE), puppet, make alliances, whatever you want basically, then just casually save the game after clicking ESC. After that your save file is gonna be located in "Load Game" category, however there is a problem, its impossible to publish anything from this category, so what you need to do is to click on "I" information button, which you can find in almost any category, which will then show up a place of your save file in files, then click on it to copy it, then if you're on Windows, press Win + R, and paste location of your file into there, then it will quickly open it in files, then open "Save" or something folder (dont exactly remember the name), in this folder find a folder named like you saved your scenario, open it and you will find file with ".aoc" extension, thats what you need, then copy it. After go back to where you started in files of the game and open "Custom Scenarios" folder and after all of that just paste the save file into there. Then restart the game if it's already running, open the game and open the scenarios category, there you can find your save file named "Save" and now finally you can upload this file on steam workshop with any name and description you want. I really hope this helps

in case you cant find location of a file, here it is "C:/Users/Admin/AppData/LocalLow/JoySparkGames/Ages of Conflict"

update the game