adding files

I would really like can add files from my computer on the mod/config files or move from config or another place to other,i tried to use immersive railroading and i cant add some files,also on mods i cant add some mods from the modding options because they were for older version (1.12) when i use 1.12.2 and i couldnt add so i would like to can add manually or something,or at least to make can add the mods for example 1.12 to 1.12.2