How create warhorse?
 

Normally in Pathfinder, we can create a warhorse simply by taking a horse and adding the "Advanced Simple" template to it.

However, when I do that, everything seems to go fine *except* the horse doesn't gain the bite attack warhorses have.

It's stuck with two hoof attacks.

I tried adding a natural attack by going to "Adjust" and then "Other Adjustments" and then "Natural Attack, Primary/Secondary" but it only shows a drop-down menu with "hooves". It doesn't give me an opportunity to add a bite.

Am I supposed to do something else?

You will want to select a heavy horse. HLC is doing what the advanced template does; +4 to all stats and +2 to natural armor. The template doesn't normally add an attack, such as the aforementioned bite.