Root rot treatment is possible, but if you want to save the plant you must act quickly in order to give the best chance of survival.
Take the plant from the soil and wash the roots under running water. Be gentle and try to wash away as much soil as possible. Trim the affected roots with a sharp, clean pair of scissors along with some of the leaves, so the root does not need to support as many leaves.
For potted houseplants make sure the container has good drainage and only water the plant when the top of the soil is dry. Don’t fertilise the plant once it has started to re-grow, as this may stress it. Hopefully your plant will recover from root rot and you will be able to enjoy it again.