Hello czlowiek_kon!
The best way to accomplish this for saving would be to use the FPaths lib. You can get project and engine-defined paths this way. Personally, I like using Project save path. See this attachment which would save to “{Game Install directory}\Saved\MyStructSaved.csv”:
If you already have a csv you’d like to include with your packaged game, you can either include it unpacked with your game’s installation and use FPaths to find it, or you can pack and cook it using the /Game/ style pathing. You just have to be sure to include the asset in your packaging settings with “Additional Non-Asset Directories to Package” under “Advanced”.