Try washing with bicarbonate of soda mixed to a paste ,apply leave overnite then rinse off well .If material is stiff and hood or apron seems to have shrunk then spray several times with solution of mixed up fabric softener then gently stretch back to fit and let dry in place .

Unfortunately there is no way to get mildew of anything you can try wasing it but it will still be there,you get get some seat covers to hide it.