Take out the cigars and give them a good wipe down, then pop them in a ziplock. Wash your tupperdor thoroughly (even the silicon seal in the lid) and chuck out the old Boveda. Pop your cigars back in the tupperdor with a fresh Boveda...then do the process all over again when mold returns, as there is no foolproof, 100% guarantee that your cigars will never get mold again.
It is just something that happens from time to time.