You don't have to make one, the game should take care of it as long as it has the rights to write in your AppData/Local folder.
You'll have to find what's preventing the game from writing to that folder, I can't provide much help with that since the issue is on your side. You can try running the game as administrator to see if it changes something and check if your antivirus isn't blocking it.
Wait a minute, that's not your first time running the game, right? I can see you commented a few month ago.
Are you sure you can't find that folder? The AppData folder should be located in C:\Users\[your windows username]\, it's a hidden folder. If you have already successfully run the game, the folder should exist, but the UserSettings.ini file is probably corrupted. Once you've located the folder (ask google how to find the AppData folder if you're having trouble), navigate to AppData > Local > Debucon and find the UserSettings.ini file. Open it with notepad/notepad++/your preferred text edition software, and copy its content here. We'll figure out how to fix it.
I'll look into implementing a foolproof in-game fallback solution in case of corrupted save files. It should be a rare occurrence, but better safe than sorry.