What can i use to clean my portable ice maker. It smells like mildew.

I have cleaned Manitowoc ice makers and their company specifically made an ice maker cleaner and sanitizer. Try a google search for this product.

When cleaning a portable ice maker I would use some warm water with a little bleach or vinegar. This will kill any bacteria that's hanging around. You could also wash the inside walls down with some soap and water. Make sure that you rinse your unit with water to make sure all of the cleaning solution is gone.

https://icemakergeeks.com/how-to-clean-your-countertop-ice-maker/