Oh my gosh!! Wooorrked!! It's installed a 9.1.0-20 instead the 9.0.0 I've downloaded.
Download the right n3ds cia files (or extract it from the ttp)
Create a "updates" folder on your root of your sd card
Copy all cia files in there
delete 000400102002CA00
Install the newest sysupdater homebrew
Use menuhax
Try to open sysupdater and try it as long as it doesn't pass step 8
If it pass Step 8, Downgrade by pressing Button y
Many tryings to work..
Thankyou @Ptrk25 for the steps.
Did it delete all of your previously downloaded stuff?