It uses standard PRC Crafting menu:
From class radial menu (every base class should have this item) select 'Examine Recipe and Craft Item/Craft Item' and target your character. After a while a conversation will pop up with all item types available for crafting. Search for 'poison' or 'alchemical item'. When you choose what you want to craft, another list will be generated containing all poisons/alchemical items. If you click one and your crafting skill is high enough and you have the required amount of gold and experience points, the item will appear in your inventory.
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