Ill try to explain better with pics:
https://i.imgur.com/A4EyY44.png
The step 65 tell me to do a valley fold following the blue line here (don't mind the other one, result of many tests i did trying out) and then reverse fold it inside:
https://i.imgur.com/MD6r9E7.png
You can see the crease on the right and the other side one on the left, that is the part i have to reverse fold few time to manage to finish like this :

(i tried to keep the screenshot minimalist to not be out of rule)
I know it will probably be impossible to understand for people which doesn't have the diagrams or never folded it but i hope some people here did folded that butterfly. And sorry for link as pics, pics were too big to display on the Forum it seems.
Thanks for help guys !!