Lo-Fi Games

I did everything I could, and I still got the error occurs while loading save

No errors of note in the logs unfortunately, but I do note you're using incompatible mods (Genesis, Reactive World, and Living World). I would suggest disabling two of those, then importing your save.

Otherwise, you can try this guide too, see if it helps:
https://steamcommunity.com/sharedfiles/ ... 2789171241

What program do u used to open FCS file

The FCS is the program, it stands for Forgotten Construction Set, which is the modding tool for Kenshi. You can find the exe file for it in your main Kenshi folder, or if playing via Steam it is the modding tool option in the launch popup.