If no milk kefir drink is being prepared, the grains can be stored in a non-metallic container in the refrigerator crisper, in a sufficient amount of milk in order to cover the seeds, while
making sure to leave some space so that they can have enough air.
You can also dry the seeds on a clean cloth in the open air, covering them with muslin in order to avoid dust to enter. You can store them in a cupboard, in a jar covered with a muslin held by a rubber band. In order to reactivate dried milk kefir seeds later, they must be soaked in lukewarm water for a few hours.
Another solution is to freeze the milk kefir seeds and then let them defrost in the open air.
Dried milk kefir seeds and the thawed ones usually take longer to reactivate, so you need to have patience.