This issue was already discussed last year. I can quote my post from there.
"To moisturize dry stuff, you need to provide it with some moisture (((
The question is how and how much?
Putting pieces of apple or other edible products in a closed jar is stupid advice, because this is a substrate for the development of mold; it is better to place on a piece of foil or a plastic lid of a suitable size any moistened material inert to mold - a cotton pad, paper, fabric, mineral wool.
The amount of moisture required can be calculated quite accurately if the hygrometer readings in a closed jar are known. For every 100 grams of herb you need 1 gram of water to raise the readings by 5%. If you don't have a gyrometer, you can simply add 1 g/per 100 g and stop or add again based on the result. Depending on the specific conditions, the process of moisture redistribution may last several days. "