How to get mold smell out of a room?

I'd have you clean the surface the dishes were on. Use a real cleanser - Mr. Clean or similar. Then wipe the surface down with an odor remover - that can be as simple as a lemon juice/water mix, or a baking soda/water mix, or white vinegar/water mix. Any of those will work. They'll remove any remaining odor on the surface.

Then, if you still smell the smell, it's not that surface - there's something else in his room. I'd do a sniff test and try to determine the actual location of the odor, then remove it and clean that area.

Obviously, you'll need to have a serious talk with your roommate.

Someone suggest you light a scented candle like Cinnamon. I prefer eucalyptus.

I'm a janitor and when the rooms start smelling like mold, I use a product called ORDOBAN. It can be found at Home Depot. It is concentrated and dilute for a spray bottle. Spray the rooms wall, floor and just the 'air'. It has a mild eucalyptus scent and last for weeks. It is great for bathrooms too.

You are going to have to blitz the place. Start by vacuuming the whole place, including ceiling's and walls then wash worktops with bleach and a scourer. You will have to look into every nook and cranny just in case there is some festering food you overlooked on your original clean up which might still be causing the smell

Coal/charcoal can help absorb the odor. Put some, or maybe a lot, on a container and place it near the source of the smell.