I guess what you should do depends on whether or not you want to keep worms in the tumbler. I have an indoor worm bin, so I don't worry about temperature, but I have read that many people freeze bottles of water & put those in their worm bins to cool things off.

I hope that helps.

Worms can't live in a tumbler. Tumblers encourage thermophilic composting, in which temperatures get high enough to kill the worms. That assumes the tumbler is full of fresh material and you are turning it every day. If the compost in the tumbler is finished, and there are live worms in it, dump it out and let the compost cure. If you can tolerate the smell for a few days (or longer?), the worms will decompose, but the remaining worms will also die if left in the tumbler.

You say you have old compost mixed with new scraps. If there are enough new scraps in the tumbler, it will heat up. Also, the worms don't like to be tumbled, even if the tumbler does not heat up.

Dumping the contents will not guarantee that the compost won't heat up.

So you can unload the tumbler and hope for the best, or you can run your tumbler like normal and figure that the worms will all die.

Wetting the compost down may cause it to go anaerobic, which will defeat the purpose of the tumbler, which is to aerate the compost every day.

Never had compost that was finished have a bad smell, so I'm guessing it's not finished. At least, not a really strong bad smell.

For the compost, add browns to control that smell. Maybe some lime if it's really bad and you have offended neighbors or an angry spouse. Decomposing worms are a nitrogen source.

For the worms: As sbryce said, tumblers aren't for worms. At least, not if used for its intended purpose.

Thanks everyone for the replies. I have learned something new. I never intended for worms to be in the tumbler. It just happened by accident because I mixed old compost in with the new stuff and some worms must have been in the old compost.

I will dump it out on to the other compost and let it sit. I use a tumbler because it is the best way to break down kitchen waste (for me) and to keep the wild critters out of it.

BTW, the bad smell came from the dead worms. Smells just like a rotting gopher. Neighbor's cats keep digging those up after I kill them. Yuck!

Thanks again.