I don't own one but looks like it has an inner liner that's not removable. Unfortunately, that's a very poor design and hard to clean. AT least with old Masuri helmets, you can remove all (velcro'ed) pads and put them in the laundry and wipe down the inner shell with an anti-bacterial wipe. I think old masuri helmets were awesome!
If my assessment is correct and you can't remove the inner liner, sun exposure is a good way to eliminate odor (or bacteria). Basically, leave the inside of the helment exposed to the sun light for a few hours and that should do the trick.
Another approach I heard from a vendor is to put it in a dishwasher and then dry it in the sun. I never tried it though.