Since symptoms of root rot mimic other plant diseases and issues, you'll need to look closer to determine the problem.
The first step to curing root rot is to get your plant out of soggy soil as soon as possible.
You'll need to cut plant roots back until only healthy roots remain.
With the plant's roots reduced, you'll need to prune back leaves to reduce the demand on the root system.
Be sure to disinfect your plant's pot, too, to get rid of the spores that cause root rot.
As an added protection, disinfect the roots with hydrogen peroxide.
When you repot your plant, use only quality potting mix to do so.
You can take cuttings from a recovering plant just in case the first doesn't make it.