So the Super 7 event proper, is located a bit West/Left of the main Horizon Festival.
For this achievement, you need to complete 7 different challenges.
These vary in difficulty, but harder ones can be skipped by pressing RB. This is doable even if you've entered into the challenge: just quit event, then 'burn card' (RB) when you get back to the cards menu.
As the challenges you're given are user created and not a standard set from the developers, it's impossible to give a guide for each challenge.
Once you complete all 7 cards in the Super 7 menu then the achievement should pop
If you have any questions drop a comment and I'll try to help