HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

The mod automatically fixes the bug, even if you simply load a save file with the bug in the mod, which occurred while playing without the mod. In most cases, it will fix itself. If it doesn't fix itself, you need to hover the cursor over the buggy object (a hero's duplicate, the entrance to a gray castle) and press the left Shift key + F2.
If the bug has already caused problems, it may not be fixed, so it's best to fix it immediately, or even better, just play with the mod and avoid these problems altogether, especially since the current settings allow you to achieve maximum comfort.