I don't think you need to delete the save folder. But it is inAnother thing I realized is that the old save was still there even though I had deleted the entire folder, I don't know if I should also delete it, although I don't know where it is located either.
C:\Users\[UserName]\AppData\LocalLow\ApplePie\MonsterBlackMarket\SaveData\
with some variation possible depending on your operating system.