First of all, nip in the bud, and remember to hang it in a dry and ventilated place after blowing! Avoid exposure! Otherwise, the gourd and the supervisor will be broken!
If you have mildew, according to my experience, a cotton swab dipped in medical alcohol (edible wine substitute) can kill mildew! Dry it with a dry cloth and hang it in a dry and ventilated place. Removable, it is best to blow dry the inside with a hair dryer!
If you really have no choice but to change the gourd, it won't be too expensive!
Good luck!