Where is the cabin air filter on 2004 Ford F-150

On a 90,ooo mile tune-up, it refers to a "cabin air filter". Where can I find the cabin air filter?

Asked by for the 2004 Ford F-150
Per the shop manual, the air distribution system on this 2004 F150 cannot have a cabin air filter. Disregard the recommendation, as it does not apply to your truck.