If you train BJJ long enough, you’ll eventually have one of those days where you come home exhausted and accidentally leave your rashguard and gi in your training bag. When this happens you may have a hard time getting the odor completely out of your gear. Your best option is to throw it away! It’s probably time for new gear anyway! Google search rashguards or BJJ Gi and then on the various websites check their sale or clearance section and buy a new one. Check out Elite Sports for discount BJJ gear and also check out a Texas based company called Ground Fighter and see what they have on discount/sale.
If getting new gear is not an option for you at this time then check out this 1 minute youtube video on how to get the smell/odor out of your rashguard or gi: