Open campaign in the editor.

What version of "Heroes" do you have? The "Chronicles of Heroes" Campaigns, like all story campaigns, are "hardcoded" into the resource files (*.lod), which are essentially archives in a proprietary format. There are utilities for unpacking resources from game files, but I haven't used them and cannot say immediately where to get them. At the same time, all "Chronicles of Heroes" campaigns are also available as separate *.h3c files, which can be opened with a standard campaign editor and from which individual maps (scenarios) can be extracted.