No pics?

It need to be cut out. Dried for 5 days, and then repotted.

I hope this plant comes back from this rotting attack. What soil is best for desert rose?

Plant is showing obvious signs of stress once vibrant green stems now pale brown with patching, the base of the plant feels spongy, I'm gonna try and chop off the rot or is this to late?

Dig it up, and take a look at the roots. Spongy and brown roots and causes are a bad sign.

It appears you are using regular potting soil. This is okay if the soil is allowed to dry out completely. Water logged soil combined with cool temperatures can spell very bad news for Adeniums.

I keep my Adult plants in a gritty mix to prevent over watering. My gritty mix is equal parts granite chips, calcined diatomaceous earth floor dry, and fir bark.

My seedlings are growing in a 50/50 mix of floor dry and coconut coir.

What zone are you in, best to add it after your name to give us a clue. Soil as mentioned is far to water retentive. I don't like the look of those tan coloured patches on the branches, are those soft also?