If it's the aroma hop addition, then treat it exactly like you would an aroma hop, anywhere between last 15 minutes and flameout.
If you decide you need some more later, like in secondary, steep it like a tea in 2 cups of boiling water. Put the chiles in a heat proof container, bring water to boil on the stove, as soon as it hits boiling, pour that in the container on top of the chiles. Steep for 10 minutes or so. Then either add everything, including the reconstituted chiles in the primary or secondary, OR strain them with a sanitized strainer.
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