The save folder is ~/Library/Application Support/KADOKAWA, and you have to rename your file by adding a prefix RPGMVLustEpidemic (e.g. file1.rpgsave -> RPGMVLustEpidemicfile1.rpgsave)You have to save firstly. You will see a save folder. Remove your save and replace it with everything you have in your older update's save folder.
Good luck