How can i get the smell out of retainers?

Retainer Cleaner: Regular brushing of the retainer with toothpaste helps, but a professional retainer cleaner can be helpful too. Ask you orthodontist which product they recommend. They usually have samples for you to try and determine if you like it prior to purchasing a product. In a pinch, hydrogen perioxide can be used to clean them by soaking them in a cup of it. Always rinse and brush them after soaking.

Fungus: The plastic is probably impregnated with fungus. Soak retainers in 1 part chlorox to 4 parts water for 2 hours. Rinse well then put into denture cleaner (pollident, efferdent, etc) for 30 minutes. Rinse well--smell should be gone. Brush retainers gently every time you brush your teeth. Put them into denture cleaner 1x/day for about 30 minutes. Do the same for your retainer case.