You can sign up for the Ninja Academy - Segging Academy.
https://nssacademy.weebly.com/
After you enroll and enter your information correctly, you’ll be added to the waitlist.
When it’s your turn, you’ll get an invite from a Sandbox Sensei in your Viki inbox to start the Sandbox training.
The Sandbox consists of different “levels/sands”, with an exam at the end.
If you pass the exam, you graduate from the Sandbox and go on to the waitlist for level 1 of the Ninja Academy (you need to graduate from the final exam after level 5 to become a segmenter).
Maybe this thread can give you a bit more information about the NSSA: