How to add "stench" as an ability?
 

I looked through the feats, traits and spells. I cannot find what I'm looking for.

Stench (Ex) A creature with the stench special ability secretes an oily chemical that nearly every other creature finds offensive. All living creatures (except those with the stench special ability) within 30 feet must succeed on a Fortitude save (DC 10 + 1/2 stench creature's racial HD + stench creature's Con modifier; the exact DC is given in the creature's descriptive text) or be sickened. The duration of the sickened condition is given in the creature's descriptive text. Creatures that successfully save cannot be affected by the same creature's stench for 24 hours. A delay poison or neutralize poison spell removes the effect from the sickened creature. Creatures with immunity to poison are unaffected, and creatures resistant to poison receive their normal bonus on their saving throws.
Format: stench (DC 15, 10 rounds); Location: Aura.


I want to add that to a dwarf.

How can i do that? I looked in everything in the "adjust" and "condition" tab as well as the places mentioned above.

You can use the editor to create an adjustment and have that add stench by bootstrapping it.

I was able to customize a Dwarf NPC on the Background Tab (or a PC by changing to an NPC, adding the customization, then changing it back to a PC), adding Stench to Special Abilities. On the other hand, I'm not sure which package(s) gave me that ability; I have a lot of content but not all by any means.

That would also work. Stench is a universal ability so I believe it should be available even just with the core rulebook package.