I'm not able to help you these days but I know the instructions.
(GW user)
Provide your .sav.
If your .sav comes from .3DZ, you need to provide the ROM header.
(MT-card user)
Copy .sav to MT's MicroSD and replace the old file.
If you receive the ROM header, you need to inject it to your ROM and rename .sav into .zav.
After that, load that ROM with select button, then run SaveDataFiler (CIA version) to export the CTR cart's save.
Done.