If you have ever backup any 3DS game bigger than 4GB, than you know if you get split files. (Examples: BACKUP.3D0 and BACKUP.3D1) I have provided a tool that many have requested and will merge files into a .3ds file. This utility can backup, restore, merge and sort.
1. Backup Game with gateway 3DS and remove SD card from 3DS.
2. Run Gateway 3ds SD Manager and select Browse to set a directory where you want the merged file at.
3. Select Merge 3DS roms and browser for BACKUP.3D0 and BACKUP.3D1
4. After you have selected all the parts to your backup finally run Merge. (Recommended merge one backup at a time)
5. You will get a window prompt that says Merge has started. Click ok to begin the progress.
6. You will be greeted with merged complete and move it on the Gateway SD card.
7. If you want online features simply change the extensions by renaming .3ds to 3dz.
Gateway 3ds SD Manager
https://mega.nz/#!Ct5SRTaJ!R2Y9zOwhP1pt ... UhtOiSxTPk