Should be simple. Check the example at the bottom of this page: http://zorro-trader.com/manual/en/ta.htm

It says: BBands(series(price()),30,2,2,MAType_SMA); meaning that's the Bollinger Band of the price series.

As you would like to apply BB to the Stochastic indicator instead of price, just replace price() with Stoch() call and that should be it. Stoch() parameters are explained on the same page.