By default Milliman Mind will automatically detect if your model is stochastic and turn on stochastic calculations.
You can change this setting in the Settings popup:
Then look at the Stochastic Run setting.
You can also choose to lock the seed, then select if you want to run every simulation or only one.
If you lock the seed, you can choose a specific seed to reproduce the same calculations. A number between 0 and 1 will force quantile.
You can also choose to run a specific simulation number by turning on the Run only one simulation switch. The number of simulations to launch in the action bar will be replaced by the sim. number.