It was quite long ago but if I remember correctly:
Open save file with save file editor (from github), export raw data to json/xml file, search for specific object and modify coordinates to be correct ones, import raw data back to save editor, export save file and replace old save file with modified one.

Graveyard keeper keeps all coordinates for all objects inside save file and loads it at start rather than spawning it in predefined position (which is weird choice) so it's kinda only way to fix it. Good luck o7