Having the heat dry isn't recommended, but if it hasn't already cracked it, just turn it off and let it air dry. Hopefully the heat hasn't changed the physical properties of the cover.
Have used the dishwasher several times, both with and without detergent. For me, it seems to work best with just a touch of detergent, warm wash, and air dry without heat.
ALWAYS TURN OFF THE HEAT DRYING OPTION
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