Using BiB isn’t simulating, it uses the data from millions of simulations to give you a gear set in a couple of seconds.
If you want to run a simulation to verify, or to check other things you can from the Simulation link at the top of the page, there’s a manual for it on the forum.
Simulation is quite time consuming so you might want to play around with BiS instead, limit the gear it can use to about what you’ve got and you can change your covenant via the menu/Hamburger icon which is to the left of your characters name.
