DIAGNOSIS: The air filter is behind a front or side panel that slides or pops off, not immediately obvious.
FIX: Turn the unit off. Look at the right-hand side (when facing the control panel). There's a textured panel. Grip it at the top and bottom and pull straight toward you. It's a bit stiff. The rectangular foam filter is right behind it. Rinse it under lukewarm water, let it air dry completely for 24 hours before reinserting.
IF THAT DIDN'T WORK: If the panel won't budge, you might be pulling the wrong one. Do not force the main front grille. The filter access is specifically the small side panel, about 8 inches tall.
HEADS UP: Running without the filter or with a wet filter is a major cause of evaporator coil clogs and ice formation. Dry completely.