The plastic smell of the cooler itself should go away after washing and leaving open to dry. Use a mixture of baking soda and water to wash, and rinse well.
If the smell is from the velcro, then it's actually from the adhesive as previously mentioned. But the adhesive itself shouldn't stink, just the volatile carrier which can be evaporated with a hair dryer. It may reduce the adhesion, however, so only do enough to eliminate the odor.