It is no secret that very often you can find orchids in a flower shop at a markdown. This means (not always, but often) that the plant spent more than a month in a flower shop in the most difficult conditions of overflow, hypothermia and lack of sunlight. As a result, there is almost no roots.
So I could not resist, and bought cymbidium at a markdown. The plant has become very sorry. When I pulled it out of the pot, it was in this state.
The roots below were healthy.
But from above they turned out to be rotten.The roots of cymbidiums are very fragile and easily break, rot forms in the places of breakdowns, so if the root breaks, it must be cut off at the place of scrapping and wiped with alcohol or sprinkled with coal .
Rotten roots need to be pruned to healthy tissue at the root. Healthy roots are yellow, elastic, hard, rotten - hollow, black, soft.
For transplantation, I took a translucent bucket (or orchid pot) and made holes there for better air access.Or you can plant in clean bark or with the addition of moss and peat.
After purchase, cymbidiums need to be transplanted, since very often insects and snails are present in the ground, the roots are often rotten, and the substrate is too moisture-intensive.
Since cymbidium is a terrestrial orchid, it also needs light land for terrestrial orchids. I bought in OBI.
To get to the middle and remove the rot there, I had to divide the plant (very carefully).
Here are two neat bushes in the end. It is necessary to let the wounds dry for 10 minutes, and if the roots were raw - for several hours.
After that, it is imperative to pour a sufficient layer of drainage into the bottom. And place the plots with directed new growth in the middle of the pot so that the plant has room to develop before the next transplant.
Then it is necessary to cover the substrate so that the bulbs are on the surface. Do not water the first 4 days. 
Here's the end result. If you are unsure that you can water correctly, make holes not only at the bottom, but also in the walls of the pot.Author of the article Anyanya