All of this is done in the Heroes III campaign editor. The campaign editor, h3ccmped.exe, is located in the root folder of the game. 1) Right-click on the selected area of the map and enter the scenario properties. 2) On the "General" tab, click the "Import" button, then select and insert the desired map. It is unclear whether it is possible, and if so, how to create your own general campaign map, because in my case, for example, the campaign names are already built-in in h3ccmped.exe, but this is a minor issue, as maps can be successfully added and campaigns can be created based on existing maps.