DIAGNOSIS It's not obvious. The filter is a flat, mesh panel located behind the front grille, not the bucket area.
FIX Unplug the unit. Look at the front, below the display. There's a vertical grille. Grip it firmly on both sides and pull straight towards you. It should snap off. Behind it you'll see the rectangular filter. Pull it straight out. Rinse it under lukewarm tap water, gently scrubbing with a soft brush if needed. Let it air dry COMPLETELY before snapping it back in and reattaching the grille.
IF THAT DIDN'T WORK If the grille won't budge, you're probably pulling at the wrong spot. Don't force it. There are plastic clips at the top and bottom. Try inserting a flat plastic tool (like a guitar pick) into the seam at the very top to gently release the top clips first.
HEADS UP Never run the dehumidifier without the filter. It'll clog the evaporator coil with dust incredibly fast, killing efficiency and potentially causing it to freeze up. Cleaning it every few weeks in a dusty environment is key.