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Would it be possible for you to post some pictures of the plant for us? Please take the pictures in good light, and provide different close-up views of the plant and the damaged areas.
([url=https://www.helpfulgardener.com/forum/viewtopic.php?t=3724]Instructions for posting pictures on the forum[/url])
First of all, there are a number of different cacti and succulents commonly known as Desert Rose. Treatment for the problem could vary, depending on which one you have.
In addition, it will be helpful for us to see the actual damage, in order to provide the best advice to you.
Just offhand, it sounds like the plant is suffering from rot. Although rot can rarely, if ever, be cured, new plants can sometimes be started from cuttings, if the rot hasn't progressed too far.