How to clean the inside of work boots? EMERGENCY!?

Somebody please tell me how to clean the inside of mens work boots! My fiance has some carhartt waterproof boots, and the inside smells like a mix of sulfer and ****. It is horrible, and I am pregnant so the smell expecially makes me want to vomit lol. The outside is pretty easy to figure out but I need to know how to clean the inside of them. please please please let me know asap thank you :)