I read the guide, and I saw that :
«Section V - Restoring 3DS #1

@Plailect
«Section V - Restoring 3DS #1
- On 3DS #1, complete initial setup
- Do one of the following (or neither if you don't mind *3DS #1's** NNID being nonfunctional)*
- Do the rest of the sections and then the full guide on 3DS #2, then wait one week, then System Transfer from 3DS #2 back to 3DS #1 (remember you cannot transfer back from a New 3DS to an Old 3DS)
- Go to the settings and attempt sign back into your initial NNID, then call Nintendo and ask about the error you get
- Reboot 3DS #1 while holding Start to launch Hourglass9
- Go to SysNAND Backup/Restore and restore SysNAND from sysNAND-A9LHAX.bin»
@Plailect