It’s important to make sure you know what something is before you remove it from the object – it may well be mold, but it might also contain evidence about the manufacture or history of the corn husk doll. I would examine it well with a good light and some magnification before doing anything irreversible. Then I would write a clear description and take photographs.
If it really is mold, then it would be sensible to put the object in a drier environment until the mold is inactive (it needs a certain amount of humidity in the air to grow). It will become powdery and shrunken as it loses moisture. The inside can then be gently cleaned with a soft dry brush (like an artist’s watercolor brush)and the loosened, powdery mold can be vacuumed away using the crevice tool of a vacuum cleaner which has a HEPA filter. Cover the nozzle of the crevice tool with a piece of fine net or pantyhose held on with a rubber band. This will stop any tiny pieces of the corn husk doll which may detach from being sucked into the vacuum cleaner and lost. Do not try to vacuum the doll, the suction will be much too strong. Use the brush to gently dislodge the dried mold and have the vacuum nozzle a little distance away to catch the mold particles. It helps to have a colleague control the vacuum nozzle.
Clean the brush occasionally on the net over the vacuum nozzle and keep gently brushing the interior of the doll till the mold has been removed.
Examine the inside carefully again, write down what you have done and take more photographs. See if you can determine why the mold grew there. Your actions and records are an important part of the history of the object.
Dispose carefully of the old tissue paper the item was packed in and take care not to return the doll to the kind of damp conditions which enabled the mold to grow.