In order for you to get this achievement, first you need to do the 2 race Rookies Cup. Simply finish these and afterwards you will have the opportunity to start a new season and compete in the Moto3 championship. Choose “Compete in Moto3”, choose a team and once in the Rider Career menu you can start the Moto3 career. I don’t know if its dependent on your ranking, but after I had finished the first 6 races in 1st place, I was asked if I wanted to stay with my current team or move onto the Moto2 class. You’re still technically gonna be racing the same races you were in the other class so once you start your Moto2 career, you will be starting on the 7th race, not completely starting over. When you win your first race in your Moto2 career, the achievement will pop.