If the weather is cold where you are, keep the plant warm at all times, even while washing off the roots. This is not the season to repot, but I would remove the whole plant from the pot, rinse off the soil, and cut off all mushy parts. Then remove unsightly leaves. Let the plants roots dry out for a few days. If you are sure no rot remains, repot in a light, well draining soil. Keep the plant indoors with bright light, Water only when the soil is very dry.
If this was an expensive plant, I would tell the seller what you found. He may offer you another plant.
Johanna

I think the question has been answered. You already knew what to do. Norma