I live in SE Michigan. I bought a plumeria cutting and was told put it in sand and follow the directions (which I did) and now My new cutting is soft about 1/2 way up the stem. It has 3 beautiful 1 1/2 inch leaves sprouting from the top. Can I cut it just above the soft spot and replant? I've read the softness is d/t stem rot caused by a fungus. Or can I treat it with something?

I have rooted them in plain potting soil. Cut it several inches above the soft spot. Lay it aside in the shade or low light so the cut can callous, harden off.
Then just stick it in soil, not too big of a pot and it will form roots. Do not water it.

Hi! MaryM56; Welcome.

Yes cut it above the soft spot making sure the soft parts are all gone.

I've cut the stem and have it sitting out to callous. Do I let it sit unattended until the end is hard? Once it's calloused...(does this take a few weeks?) what kind of soil do I put it in? I was told sand but I'm questioning if that was right since the stem rotted. The sand seemed to be moist underneath the top layer, which I didn't know until I pulled it out to cut. Please advise. I bought this cutting because they said they are easy to grow ..... 🤷🏻‍♀️I'm willing to work and get it right !

While I spent 9 years in Florida, I just used conventional potting soil. I watered the cuttings very little until I saw new leaves really underway up top!

My plumeria has calloused and so I re-potted this mor but the stem appears to be "shriveled ". What does this mean? Do I need to do anything? Is it dehydrated? Help!

Well of course it's dehydrated.
The plant suffered from rot and you made a cutting. You got into good, viable clean tissue and replanted. There are no roots for it to have taken up any water. Once it roots, it will plump up as it absorbs water.