Root rot, what to do?

[Anna]

Hello,

I got a big Cymbidium a couple of days ago really cheap. Unfortunately it was kept outside in the rain and cold. The plant looks ok, foliage is green but has 3-4 strange black spots that don’t seem to be getting bigger, a couple leaves are turning yellow but maybe they’re just old. The pseudobulbs seem healthy, but the roots aren’t happy. The medium is soggy and almost 90% of the roots I can see are rotten. I don’t know if I should repot it or not. It has 3 healthy looking new shoots growing. I really don’t want it to die!