The simulator can be accessed in the Safe House. It is the column with the chairs around it.
Simply enter the sim and create a beasting custom load out (you can pick from all guns and grenades). Make sure the difficulty is set to recruit to make this easy. Then just survive the 16 rounds.
You do need to be quick and finish rounds as fast as you can. If you don't you won't get enough points towards the gold.
I did the sim in 24 minutes and passed