I have an schefflera aka umbrella tree?

how do you cure it;'s root rot?

I have an schefflera aka umbrella tree?
I would start by transplanting out of the current soil it's in. Trim away as many rotten roots are you can, and try to shake as much soil out of the roots as you can. Repot it in clean soil, making sure the pot's drainage hole is open and not clogged by dirt (try positioning a rock or two angle-wise in the hole to prevent it from getting clogged, but still allowing water to flow out). Then give the plant a pruning - remove at least as much green growth as the root growth you pruned off in transplanting it. Then water the plant just enough to wet the soil and send a little bit of water into the pot's saucer. You don't want the plant to be sitting in water, so if you over-water and there is a lot of water in the saucer, pour it out and replace the pot in the empty saucer. Keep watering it in the same manner, trying to avoid letting it sit in water. Root rot thrives in water-logged soils, so avoid this condition and you should be ok. Good luck!
Reply:the only addtitions i would make to molly's suggestion is that you also thoroughly rinse the roots before repotting the plant, and use b1 solution in your final watering.