You click on one of the pandas, click on the tab with the plant symbol in the animal's window first. It'll show what the panda thinks about all the different plants in the habitat. Find and delete the plants that are in red boxes, as it means the panda doesn't like them. Then go to the bar at the bottom of your screen, while still having that same tab open for plant information by your panda. Click on the button with a plant, the nature tab. Use the filter options to select the continent and biome the panda prefers, per that panda's plant info. Add enough plants that the panda likes until both of the plant bars in the panda's window are in the green somewhere.
